There are several ways to earn boosters.

  1. Collect your daily bonus for a chance at finding a booster.
  2. Earn stars: each one of them gets you a booster.
  3. Take part in events and competitions. The treasure chests you get as a reward for winning may contain boosters.
  4. You can buy sets of diamonds and boosters in the Store as an in-app purchase.
  5. You can always use diamonds to buy boosters before a level starts or during the game.