First, I build up the economy, skeletons-archers, zombies, then a level 1 town guard and a watchtower.
In the second week, I build liches, vampires, a converter, and messengers (if I have enough resources).
Then, I upgrade the fortifications and build ghosts.
And finally, I focus on magic and upgrades (it rarely gets to dragons).
If there is already a fortress in the town, the strategy changes. I build ghosts and increase the growth rate.
As for abilities, I prioritize necromancy, darkness, chaos (or summoning), education (mana attraction, cold reward), and defense (the hero will mainly attack with magic, and the army must be resilient), and spellcasting.