Your strategy for playing as Necropolis.

Strategy: Develop necromancy. Gather skeletal archers; for the first two weeks, you can manage with just zombies and archers.

Dear user, you should have installed patch 1.5 for the original game and 2.1 for the expansion pack a long time ago – they significantly nerfed necromancy, and it becomes very difficult to build an army in the early weeks...
The best thing you can do is to upgrade Spiritual Link as soon as possible and use Resurrection until the enemy is almost dead... This allows you to make good progress against moderately strong enemies... The main thing is to build ghosts and vampires as quickly as possible – ghosts for their immateriality, and vampires for their vampirism – 5-15 vampires are already a force to be reckoned with!
Upgrade attack and, if possible, defense – choose special necromantic skills – Cold Steel, Haste, and Grave Chill – and your undead troops will start performing wonders :)