I don't think icons for games are that much different from any other icon. You want it to be clearly recognizable and well.. iconic.
Integrating an icon into the games art-style is basically the same as creating an icon for any existing platform. You'll have to respect the art-style that has been established for that platform (example: have a look at the Windows guidelines or Mac OS X Guidelines). For your game you can come up with your own set of guidelines though. It can be as simple as: Icon must have the shape of a circle and must be provided in two sizes, a big and a small version.
I'm afraid there's no guide to the best game icon though. Creating good icons requires a lot of talent, because you'll have to be able to reduce stuff to the max, while still keeping it recognizable and maintain a consistent style. So definitely not something that should be done by a programmer (no offense).
Maybe these tutorials are of some help to you.