Get 6 priests, 6 archers, 6 warriors and 3 wizard (6 wizards, if you can). Spend $500 on each ogre cave attack flag, one at a time and then on graveyards. You'll win quickily.
Priests are most important uy 3 rangers, then 3 warriors, then 3 priests, then 3 wizards, 3 rangers, then 3 priests, and finally then 3 warriors. Focus on market upgrades first. Another major essential is ice bolt for wizards.