Tips for development in the game.

It’s best to start playing Heroes with The Shadow of Death or The Restoration of Erathia. In The Shadow of Death, you can choose the difficulty level, and in The Restoration of Erathia, the difficulty gradually increases as you progress through the Campaigns, so you’ll learn gradually. If you have Armageddon's Blade, definitely don’t start the Walkthrough with the Dragon Slayer or Trial by Fire Campaigns. The most optimal option is the Armageddon's Blade Campaign itself; it’s the easiest in the game. Then play the other Campaigns.
I usually play like this: first, I build all the buildings (except creature generators) up to the Capitol (prefecture, market, forge, guild of mages, municipality, Stronghold, Castle, Capitol), collecting unclaimed resources with heroes, and then I build the creature generators. Of course, it all depends on the circumstances; I might build monsters if needed, but the goal is to build administrative buildings to generate a stable income, and then use that income to acquire creatures. However, I play on difficulties 2-4; I’ve only played on 200% a few times, and this tactic is only valid for maps of size M and larger, that is, when the enemy is still far away, and you don’t need to worry about a strong army yet. In two weeks, you can get a pretty strong city. The main thing is to choose a hero (or several) and level them up, level them up, level them up. Also, it’s best to try to capture the adjacent mines in the first few weeks and not wait for your opponent to develop. You also need to hire a hero and have them explore the map, and then, if possible, eliminate the opponent’s heroes while they are moving around with small armies or armies smaller than yours.
But this is for Heroes 3, and different missions have their own nuances; in many ways, the game tactic depends on the map, on the terrain on which you will play. Remember, if you manage to build one building a day (more or less) in the first week, then you’re on the right track. And don’t split your army if you can attack the enemy with a larger force. Level up your hero and magic for him; you’ll be able to win with quality. That’s basically it; the rest depends only on you.