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Arhangel93, different races require developing different skills. For Orcs, it is preferable to develop combat skills, mainly offensive ones, but these skills are not as important for Mages and Sorcerers (Dark Elves); magic is important for them (i.e., knowledge and spellcasting skills, and for Mages, I think summoning and animancy are preferable, while for Dark Elves, CHAOS RULES). Humans, I think, tend more towards defense (but, like Orcs, combat skills are more important for them, and from magic – light magic). Norkamans tend towards raising the dead, vampirism, and other dark magic skills. Runic magic is important for Dwarves. For the High Elves, archery is extremely important (for this race, it is generally best to rely on blue elven archers, and use raccoons for cover, unless you have an artifact that removes penalties to archery range – then archer masters deal more damage). Oh, I almost forgot about Demons (probably because I don't like playing as them); for them, it is important to open gates, develop offensive skills, and spellcasting. Knowledge is not as important for them as for other races that use magic because they can steal mana (with imps) and accumulate it (by draining it from the dead) during battle.
I definitely recommend developing logistics for any race – this gives your hero mobility, which is extremely important, especially when fighting against superior forces.
But this is just my point of view, and I am not imposing it on anyone; I may be wrong about something.
Added after 12 minutes
Demi, "my Zehir can't find the Tear of Ashi – I've already searched the entire Dungeon with three heroes!!!!" If you are talking about the "Call to the Dragon" mission, then as far as I remember, you don't need to look for the Tear of Ashi there, especially in the Dungeon. Zehir should act on the surface (and should go there immediately), while the Dwarf monitors the Dungeon (I don't remember his name, Wolfstan, or something like that). Zehir on the surface should gather a group of his creatures from their habitats, so you need to take them over immediately. At first, he will be fine with what he has at the beginning of the game; I don't remember the plot exactly, but in the end, a strong hero blocks his path to the portal; you need to defeat him, and it is impossible to do without additional creatures. By the way, you also need to develop the Dwarf (he is involved in the last mission, as are Humans and Dark Elves, and if these characters are not developed, you will have to replay everything).