In the first few rounds we suggest buying a farm, archers, and gunners to build up your defenses.
Ues repairs only if absolutely necessary:
try to keep enemies from damaging your casle as much as possible so you don't have to waste money on repairs.
You'll need to upgrade strength quickly to take on later enemies. Also inceasing health limits are pretty good.
Use save game:
use save game pretty liberally so if you screw up you can restart at current level.