fanmix tutorials?

Flist, I need some help. As you know, I love to make fanmixes, but I really want to make my covers better. Do you know of any places that have tutorials for covers? I tried looking myself but I couldn't find anything. For those of you who do make them, could you tell me how you come up with ideas? I only have GIMP so nothing Photoshop related please.

Any and all advice would be much appreciated. Thanks in advance! ♥