From Science Bob...

The hardest part of most science fairs is actually deciding WHAT your project is going to be. My advice is always to pick something that really interests you and something that you care about.

Also keep in mind how much time you have to do your project and how easy it is to get all the stuff you will need to do it. Follow the Scientific Method, take good notes, stay safe, be kind to animals and humans, and have a great time experimenting. Let me know how it goes...I hope you get an A+!