Rules: The one with less Power loss wins.
Technique:
1. Pay attention to unit matching. Infantries restrain cavalries, cavalries restrain archers, archers restrain infantries, and siege vehicles are restrained by infantries, archers and cavalries, but are effective against defensive buildings.
2. Advanced unit has overwhelming advantages than the basic one. It's often true that a plenty of basic soldiers can't defeat a few advanced ones.
3. Lord skills, tech, gears may bring soldiers buffs and increase their battle power.
4. The number of deployed troops is the best guarantee for victory.