1) Don't use text.
2) Don't use filters.
3) Consider your over all composition carefully.
4) Just because it's a self portrait, you don't have to use your own image.
5) Don't just throw everything your interested in into the image. A self portrait is a snap shot of some aspect of yourself.
6) Consider how color, line, rhythm, and value all create/affect compisition.
7) Consider your concept... what is the image saying.
8) Make sure it doesn't look like something you should have just staged and photographed (that is, why photoshop?)
9) Make sure it doesn't look like something where you could have printed out the images and glued them together on paper (again, why photoshop?)