You don't have to be an expert artist to make an attractive iPhone game app icon. My app, "Insect Evasion," is a game where the player must escape from attacking bugs and thus decided to star the main bug. Here's the steps I followed:
1. Start off with a few rough sketches. They don't have to be exactly the look you want, but instead give you a foundation to start your icon out with. You can then scan the image or just take a picture with your phone and email it to yourself. This is the sketch I started with, by no means a work of art, but it is a good starting point.