Small rewards are a great way to motivate your child. If you reward your child often and regularly for not thumb sucking, he or she is more likely to succeed.
Set a goal for how long your child will try to go without thumb sucking. Start with one day, or even part of a day. Then aim for longer periods. Let your child pick a reward for reaching that goal.
You can use simple star stickers on your chart or, for a more fun alternative, purchase a coloured stamp pad and let your child print their thumb print on the chart each time they reach a goal.