I've been doing graphics for about 5 years now, yes I started young heh, and I find one of the best ways to get better, is to experiment. When you see a design element you like, try to experiment using different filters, brushes or textures to see how it may have been created. Along the way you may find some unique effects you had no intention of creating but are glad you did.

And as an extra tip: When designing, always keep some of the results that may not match the exact look that you were going for, for later use. Sometimes when I'm designing something and get stuck, I look through my old files and find some great stuff that at the time had no idea could work so well with another design.