Tap the skill meter of one of your heroes and it will fill faster. Consider tapping the healing skill of the healer to keep your group safe. When facing easy opponents, also tap the offensive skills to speed the battle. The cost to improve skills gets progressively expensive. However to not save skill points because you will be too weak to face some enemies. Because all skills are important, try to keep them balanced when upgrading. Repeat missions to gain skill points, as well as treasure. Tap "Replay" on a mission that you can complete without too much interaction. You will eventually unlock idle mode, which allows your heroes to battle you are inactive.