The Merriam-Webster dictionary says that talent is, "The natural endowments of a person." So when it comes to selecting your act for any talent show, choose what you're naturally comfortable with and what you can master by the time the talent show comes around. You're the best person to know exactly what you're a natural at.
Girl Group Act
Find video of your favorite girl group and do your own rendition of their performance. It might be one of the top artists of today or from a past time. Wear the same types of clothing, hairstyles and shoes to really get the crowd going. If you can dance and sing but need help with perfecting your talents, go to a local vocal coach or dance instructor and take a few classes.
Jump Rope Act
Learn single jump rope or double dutch jump rope tricks to your favorite music for a jump rope act. Visit sites like YouTube for quality tutorials and remember safety first. If you can't do a certain trick get the help of a professional like a gym teacher.
Head to your local magic store and ask about the most alluring magic tricks. Once you learn a few advanced tricks, ask another female to be your assistant for the talent show. You'll should already have the innate ability to perform magic tricks--it's not wise to do this as an act yet if you still need to learn the basics.
If you find that you're always making people laugh, jot down a few of those things you've said that just crack people up. Time yourself and practice the jokes until you know your comedy routine by heart. Then get a few friends and your parents to listen and ask them what they liked, as well as what you can improve on. Work on the act more and have them listen again until you know you've perfected your act enough to perform in front of an audience.
Take your comedy to the next level with a dummy act, adding ventriloquism to the equation. Learn how to operate the dummy and practice speaking without your lips moving. Get a female dummy doll and ask her questions she'll answer in a way that makes the audience laugh.