You should focus on building some resource camps as to help you farm resources constantly. That consists of the Quarry and Sawmill for start, and after a couple of levels the Sulfur Mine and Crystal Mine. When you are outside the city, you will see some special areas where you can set those structures. Start by positioning five Sawmills and five Quarries, since that's the optimal variety of structures you can have till you level up the Castle to level five. Place in the staying areas 1-2 Training Grounds and also 1-2 Medic Tents once you've done this. They will help you once your soldiers get hurt, by recovering them.