Before you participate in an event, make sure that you have full energy (indicated on-screen as thunder bolts). You can tap on your bolts to fill your star meter. When you can afford to, instead of taking small actions, utilize those moves that require the most energy, which will allow you to gain stars more quickly and lead to easier success. If you start an event without full energy or you fritter it away on smaller actions, you'll likely find that you've wasted your time, particularly in later events.