I try to build Wyverns in the first week – they provide strong support for clearing the map. If I manage to build a Stronghold in the first week, I can spend everything at the beginning of the second week and buy Archers and Wyverns, and then deal with Gnolls. I don't touch Sprites until there are many of them. With Wyverns, I can clear the map successfully and with minimal losses, or even without any losses.
Sometimes, I even neglect the Town Hall.
The army is the most important thing.