Check the battlefield before committing to a formation. More often than not you will find obstacles or hazards that should be avoided.
Colosseum
When fighting the Colosseum, you do not need to tap right on the enemy to attack. It is actually more effective to use two alternating fingers when tapping anywhere on the screen to rack up more hits.
Keep fighters in front
Typical team roles apply: keep the fighters in front, and leave the less sturdy ranged units behind them for support.
