Your rewards depend on what league you're in. The higher your league, the bigger your rewards. In total, there are five leagues in the game:

Petty Pranksters
Firecracker Fans
Skilled Cannoneers
Firework Masters
Great Pyrotechnicians

You move to a different league gradually. To upgrade your league, take one of the top spots on the leaderboard. Please note that if you place low in the competition, you can lose your current position and move back to your previous league.