Before you create your rewards, you need to have your budget, and funding goal established. You should also know the persona of your backer, and the price of your product or service. This way, you can establish how much your potential backer is typically looking to spend. If you have a small product priced at $5, than do not expect the majority of backers to buy a $250 reward. You have to understand what prices your backer would be comfortable with.
Based off of your budget, campaign goal, and price of your product or service, you can establish your rewards. These rewards should start at the price that your typical backer will pay, then increase for those looking to spend more. Be sure that your rewards do not differ in price by a large margin. Each reward should be slightly more expensive than the previous.
Most importantly, be creative. Some backers appreciate being included into credits, while others prefer to have a physical product. If you understand your bakers, and have done your research, than you should be able to create rewards that will satisfy them. Ask yourself, what reward would further convince you to donate to a project?
Remember, there is no exact formula for creating rewards. The rewards are just the Cherry on top so to speak. Next up, learn about Funding