Everything available in the Castle is built within 3 weeks (it can take up to 5 weeks if the map has strong monsters). Then, buildings for griffons (forgot what they are called) are methodically captured, thereby obtaining Angels. I divide the Angels into two groups (resurrection of FTW, and I don't even take the first two units at all; it doesn't matter on HL maps). At the very beginning of the battle, I use Prayer (Water magic is almost always upgraded for me), then clones on Archangels (either a strong hit or resurrection, - 1 hit from the AI (and probably from a human too)). There is a tactic to catch the AI with blindness. Then resurrect yourself calmly and finish off what's left. Explosion, Berserk, and other strike spells are used depending on the situation. Another trick is to cast Control...
P.S. I won't mention the importance of utopias or developing secondary castles. That is already obvious.