I'd say try to vary up the styles of your sigs as well as the backgrounds (try and make one, maybe, with a brighter background). I had the same problem, most of my backgrounds looked very similar to each other.
Also, maybe try a bevel and emboss on some of the text. To do this, right click a layer and choose "Blending Options." Then, check Bevel and Emboss and select the box. You can edit from there. The best way to learn what everything does is to play around with it, for a while if you have to just until you get the hang of it.
I also suggest maybe using some filters, they can make stuff look cool as well (not TOO many, though, cause it can look cheesy).
Otherwise, VERY good work, you are progressing very quickly/
(Note: you may want to get a few more brushes, Abstract and Grunge)