Very good tips, usually work for me, and explained very well:

  1. Don’t use words on the App Icon
  2. Work with simple forms
  3. Use details
  4. Use vibrant colors when possible
  5. Don’t make promises your app does not fulfill
  6. Keep the visual language and art style from the app
  7. Test design with and without borders
  8. Get creative, do something your competitors didn’t
  9. Choose a small SpringBoard name
  10. Test the icon

So, to sum it up - being simple but standing out, being creative without over-promising and testing what you do over and over again.

Simple, no? Well, no. But it works. I know.

Full post here:
http://blog.worddata.com/app-store-optimization/10-tips-better-app-icon/