I'll outline my strategy:
- First week. Buy a second hero, and if the map is large, even a third.
Build: Graveyard, Necropolis, Guild of Mages, Crypt, Excavated Graves.
- In the second week, you need to build Ghosts and Vampires. Ghosts are good against Druids/Mages, and Vampires are used against Archers. Capture Sulfur and Mercury mines. Build a Stronghold. Upgrade Ghosts, Zombies, and Vampires.
- In the third week, if the neutrals allow, you can take a trip to another Castle. We need Ore and Wood as a priority, so we need to find them by any means necessary. Build a Castle and immediately start producing Dragons. The main thing is to use Necromancy to raise improved Liches and learn Plague. With the Pain Lord, you can rush very effectively.
- Finish building the Guild to level 3. Decide on the spells. Check the tavern - if the opponent already has a level 7 hero, build Messengers. Also, deploy Liches.
- And then - it's all simple. Turn the living into resources at the Transmuter, finish learning Master Necromancer, and by that time, you'll have a decent army.
IMHO. And I usually build Ghosts and Messengers last. It's more profitable to quickly make Liches, and also because they need the Bone Pillar, which gives + Dark Energy points.