
These are not strategies for specific maps or campaigns; rather, this is a collection of strategies and tactics you can use in specific situations.
Trees of Knowledge are nice in that visiting one gives your hero an immediate level-up. If you start a game with one of these near your town, don't visit it until you have gone up at least 10 levels. Why? Well, if your hero is at level 1, you only need a few dozen experience points to go up to level 2. Wait until you are at level 15 or 20 or so, since you will then need much more experience to go up another level. If you visit the Tree of Knowledge then, you will receive enough experience to go up another level. Visiting at a low level is a waste, since you don't need all that much experience to go up a level anyway.
If you start at the beginning of a game near water, and have a boat available, send a scout hero out to gather goodies on the water. This can include lots of gold, wood, and artifacts. Do it quickly, since other heroes will be doing the same thing. The scout hero, to get the most benefit, should have the Navigation skill, or a water movement artifact.
For a magic hero, you should seriously consider getting Expert Earth magic. This school of magic has some excellent offensive spells, namely Meteor Shower and Implosion. It also has Raise Dead and Resurrect. The most important spell is Town Portal. If you have Expert Earth Magic, casting Town Portal lets you go to any town of your choice, as long as it's one of your towns, and there is no hero currently in it. This is an excellent way of getting around on a map.
If you have the base dwelling for a troop in your town, you should upgrade it before hiring any troops. This is because if you buy the base troops, and then upgrade the structure, you have to pay extra gold to upgrade those base troops you bought earlier. A better way is to upgrade the structure first, and then buy the troops. You don't have to pay extra for upgrading the troops later. There are exceptions to the rule, however. On some maps, certain structures or their upgrades are disabled (cannot be built). In this case, you have no choice: you have to make do with what you've got. The other exception is if you cannot afford the upgrade, or you need the regular troops much more than the upgraded ones. This could be if you don't want to wait to upgrade the structure first.
If you are facing some monster enemy troops such as Archdevils, Archangels, Titans, etc, and are afraid of the retaliation factor if you send one of your stacks over to attack them, here is a solution. Have a weaker stack (Goblins, Sprites, Pikemen, etc) attack the enemy stack first. The enemy stack will retaliate, possibly defeating the attacking stack. But the defender has also used up their one-per-turn retaliation. You can then send in your heavy hitters to do damage without fear of retaliation. This will not work against Royal Griffins, as they can retaliate an unlimited number of times.
The Berzerk spell causes the target stack to attack the nearest stack, whether friend or foe. Try casting Berzerk on an enemy stack and see what happens. Make sure you cast Berzerk on the fastest enemy stack, or on the one you know will go next. If you don't, the enemy hero could dispel it. With Basic Fire Magic, Berzerk only affects one hex. At Advanced Fire Magic, Berzerk affects any stacks within a 7-hex radius. At Expert Fire Magic, Berzerk affects an 18-hex radius. This is an excellent spell to use when attacking a town with walls: cast Berzerk on some enemy stacks inside the walls, then sit back as they slaughter each other. The same goes for battle in the field, especially if the enemy made the mistake of bunching up it's stacks. There's also the fact that the enemy stacks will use up their retaliations as well, which works to your benefit.
If you've played any of the previous Heroes games, you probably know about the Armageddon Attack. Give a hero with high spell power the Armageddon spell and some stacks immune to magic or fire spells. Get into a battle and cast Armageddon until your enemy has been defeated. This will not work if your enemy's troops are immune, though. Black Dragons, Gold Dragons, Efreet, Efreet Sultans, Fire Elementals, Energy Elementals, Magma Elementals, Magic Elelementals, Firebirds, and Phoenix are all immune to Armageddon. Give yourself some of these immune troops, and go out and have fun! This tactic has a couple of uses. If a monster hero is approaching one of your towns, just send out a hero with sufficiently fast troops (so you get to go first in combat) and cast Armageddon. This tactic can weaken the enemy hero greatly. You can also do this when trying to capture a deeply entrenched town: use a sacrificial hero to do most of the job, so your main army commander can come in and mop up the rest. Beware: the computer does this too!
I think this is probably the best way to arrange your armies. The shooters should go into the corners of the battlefield (left and right end on the hero screen), and the slow/strong stacks should go right next to them. This means the shooting stacks can only be attacked from 2 directions instead of 3. Also, leaving slow/strong troops right next to the shooters gives some defensive power to those sections. If a fast enemy stack comes over and hits your Orcs, for example, your Ogres will be right there to wipe out that stack. If you don't place your shooters into the corners of the battefield, at least surround them with strong defensive units. Another thing is that you should never place your shooters directly adjacent to each other. An enemy stack could come over and block both of those shooters.
Artifacts and treasures are often hidden behind trees and mountains, etc. You can't see them, but the computer sure can! To grab the goodies before the computer does, place the horse icon somewhere, and if it turns to a rearing horse icon, there's something to be had! This applies to any map location where you can do something. If there's nothing to do, there is no rearing horse.
Never spread your forces too thin among many heroes. Build up 2 "super" heroes, one to protect your castle, and the other to go around conquering. You can have extra heroes as scouts, however. They can just go around grabbing resources and mines. Another note is to never let your castle hero go further than one turn's travel from your castle, or you may lose it.
You should always save your game before going into a battle. Always. If you do, and the battle goes poorly for you, you can just reload your previously saved game, and try again, or not bother with it at all. This also applies to other situations. You should save your game if your hero is just starting to explore new areas: an enemy hero may pop up out of nowhere, catching you unawares. You may run into an ambush (which is not common, but does happen). Save before going into a Dragon Utopia. Save before attacking a town. Get my point? Save, save, save...
If you find you are needing more troops for your army, capture a town on day 7. The next day, being day 1, will allow you to hire new troops in that town, unless it's the week of the plague.
Is a strong enemy hero bugging you? Capture one of his towns (or any town, or leave a town empty), hire all the available troops, and then leave. The enemy will almost always go straight for undefended towns. He'll leave some troops behind to defend it, weakening him slightly. Do it all over again, until the once-strong enemy hero can be easily defeated.
If you find you are not getting as much movement per turn as you would like, this is why. The whole army moves at the speed of the slowest troops in that army. This is why you generally should leave those Ogres at home, because they slow you down. There is a way around this, however. The way movement works, is that a heroes' movement is calculated at the beginning of each day, according to his army speed. Go into a town and leave all but your fastest troops in town. That is, put them into the town garrison. Stay overnight. On your next turn, move all your troops back into your heroes' army, and voila- he's got some extra movement, despite those Ogres! This works because you only had fast troops in your army at the beginning of that turn. This only works on a day-by-day basis, though. Another way to do this is to transfer troops with another hero.
One useful structure in Heroes 3 is the marketplace. It allows you to exchange one resource for another. For example, if you had a lot of gold, but needed more mercury, you can just click on the marketplace in any of your towns (providing it's been built, of course!) and trade a certain amount of gold for some mercury. The marketplace is an essential structure: besides the creature dwellings and castle, I consider the marketplace to be one of the most important buildings you can build in a castle. If you're so close to building another structure, but can't because you're short 2 wood, go to the marketplace. If you need more gold to hire troops in your castle, trade some of your other resources to raise the necessary gold. At first, when you only have 1 town with a marketplace, the exchange rate is not very good. I really only build it because you have to have it to build the City Hall. However, if you get more than one town with a marketplace, the rate improves considerably.
A trading post can be visited on the map screen. It provides the same exchange rate as if you had 4 marketplaces. Like I said above for marketplaces, these locations can be very useful if you're short a few resources. Additionally, it could be useful when you only have 1 or 2 marketplaces, and want to get a better deal.
Be careful when you cast Chain Lightning. If any of your troops are too close when the spell hits your enemies, they'll get zapped too. Also, be aware that Chain Lightning hits 4 stacks. So if, at the beginning of a battle, your enemy has only two or three stacks, the effect will hit some of your troops too.
You know how, when you have several towns, it's such a pain to go to each of them and recruit new troops each week? Here's a shortcut for you! On the map screen, access the Kingdom Overview screen. Click on Towns to view each of your towns. Beside each one, there will be pictures of the available troops to be hired there. Just click on the pictures to hire the troops as you normally would, but this works much faster.
In Heroes1 and Heroes2, you could stand in a certain place such as a stone lith so as to block people coming through from the other side. This does not work anymore, unfortunately. If you now were to stand at the entrance of a Subterranean Gate or Monolith, anyone trying to come through from the other side will attack you automatically.
If you're a good player, you'll know that visiting an obelisk on the adventure map reveals some of the map showing the location of the Grail. If you visit all of the obelisks on the map, then the whole map will be shown. However, you don't HAVE to visit every one of them! Just go to 5 or 6 or 7, so it reveals enough for you to figure out where the Grail is. Then send a throwaway hero or two to dig in the approximate center of that area shown on the obelisk map.
I have found, when you go up a level and have to choose between 2 secondary skills, that it is best to upgrade skills you have already before getting new skills. This way, you will have a few expert skills instead of seven or eight basic skills spread out, whose effects would be less noticeable.
Treasure chests are great for gaining quick levels for a new hero. However, as he goes higher in level, he will require more and more experience to reach another level. So when you find a treasure chest now, either take the gold or let one of your weaker heroes get the experience. Getting a few treasure chests' worth of experience will not be enough to help a high-level hero get another level. Visit a Tree of Knowledge instead, like I mentioned earlier!
Ever get annoyed with those slow troops of yours that never actually get into a battle? Leave them at home! Slow-but-strong troops such as Ogres, Dwarves, and Hydras make excellent garrison troops for defending your town. They slow down your hero, and take all day to get across the battlefield. However, the defense and speed is perfect for protecting the homestead. Just let your arrow towers work on the enemy!
Archangels have the natural ability to Resurrect fallen comrades. You should take advantage of that ability if you are using them. If you want to Resurrect a fallen stack (one of your own, of course!), simply click on the defeated stack (when it's the Archangel's turn), and the Archangels will Resurrect that stack completely. The Archangel stack has then expended it's turn. Note that this can only be done once per battle. It is, however, a very useful ability.
It is generally a good idea to let the enemy hero cast a spell first. Why? He may cast Blind on your Marksmen, and you won't be able to dispel it, if you have already cast a spell that round. Wait until the enemy hero has cast a spell, then cast one of your own, depending on what the enemy did.
Don't waste spell points on the Summon Elemental spells. Elementals are weaker than they were in Heroes2, and are not really worth it. A direct damage or supporting spell would be better, unless you have more spell points than you know what to do with.
In Heroes3, you have a lot of leeway when building up your towns. That is, you can build structures in many different orders. The order that I recommend for most maps is to get up to the Capitol ASAP. This gets you extra income each day. Or if you are playing on a map where you need troops right away, build their structures first, then worry about the income generators. Myself, I prefer to get the Capitol first (if possible), and then build the rest of the stuctures. However, the order is up to you.
Some heroes come with the Estate skill, which generates extra gold each day. Some other heroes specialize in producing extra gold, or other resources. You should hire at least one of these heroes, because they are basically walking mines, generating extra resources for you each day.
At the beginning of the game, it may be a good idea to put aside structure upgrades for now and concentrate on building as many troop dewllings as possible. This gives you many more troops sooner. Don't bother upgrading. Try to get up to at least you level 5 troops. You should be able to dow it in the first 7 days. On day 1, hire them all out. Then concentrate on building other structures, and getting the Castle and Capitol. The former generates twice the number of troops each week, while the latter generates more gold for you to hire those troops with. What I always do is, on day 1, hire all the troops available (or as many as possible). After all the troops are hired out, then I build structures. Anyway, then you can start building the troop dwelling upgrades, one per day, or as you can afford them. Stop only to hire new troops at the begining of each week. Before the month is out, you should have a sizeable army. Note that all the while, you should have scout heroes running around grabbing resources, artifacts, claiming mines, and so on.