Wear something distinctive to the audition. While anything overly distracting, such as a clown suit, can work against you, wearing something that makes you stand out will help keep you in the memory of those holding the audition. Whether it's bright yellow socks, a pair of suspenders or a top hat, accessorizing your wardrobe will help you stand out.
Choose a story from your past that you think is difficult for others to duplicate and that is special to you. Many game shows will either interview you or ask you to fill out a questionnaire regarding your background, and a fun backstory will go a long way in setting you apart from other contestants. Practice telling your story in front of a mirror in an entertaining way so you're comfortable expressing yourself.
Emphasize elements of your personality that you think will help you establish yourself. If you're good at telling jokes, tell a lot of jokes in the audition when the opportunity presents itself. If you have a sarcastic wit, be as sarcastic as you can without being rude. If you're a good singer, pick a moment to break into song. This helps you stay in the minds of the audition crew and will also make the audition more fun for you.