Poll: Preferences when choosing skills in Heroes of Might and Magic IV.

There are many development paths, but the essence is the same: a larger army, a stronger hero, and better artifacts.
The first can be achieved by the Sylvan and Haven factions, the second only through the player's skill, and the third is achievable with the first and second, although when you have a Rogue, only the second is enough. In general, in my opinion, you should always take a Lord, even on the smallest maps; a Mage should always increase their defense (at least to medium), and a combat unit should learn defensive spells of the first level (not necessarily Life). And then... look for trees:D
P.S. Another useful thing is an invisible scout (first-level scouting and 1-2 levels of stealth). It's not quite a Rogue, but it's enough to, for example, spy on a human opponent, guard a border, or send ahead to scout territory and capture weakly defended castles, mines, etc. With such a hero, you won't even have to send a "suicide" unit to determine the size of the enemy army.