Keep busy. You can always find something to do. The boss hates to see the waitstaff stand around.
Your pay is usually an hourly wage plus tips from the waiters. If a waiter asks you to do something, try to accommodate him. He will be tipping you at the end of the night.
Be pleasant to the customers. If a customer asks you for something, get it or find someone who can help.
A busboy can earn decent money. If you find you enjoy the hustle of restaurant work, you'll have a great start in the business.