Well, you're no competition for most artists, DBZ or not, so may I suggest studying a little human anatomy and as as painstakingly excrutiating as it may seem, it will do wonders, though I haven't done much myself. I'd also advise that you go a tad less angular and work on smoothing it up, and drawing original characters is better, less people complaining about how it isn't EXACTLY ALIKE. Here's one I drew a loooong time ago, 'bout March '06 when I was debating with another guy on why Vegeto isn't SSj2 because the Daizenshuu confirms it and he has no lightning or aura an' all that shit, but he wouldn't FUCKING LISTEN, so I had to illustrate the difference for him because I lost that Toriyama sketch when I cleared my DBZ folder out of disinterest.
Btw, here's another one I did, probably the last one I did of original DBZ characters when I stopped drawing DBZ like the way you do:
I was lazy and getting rusty out of practicing very seldomly(if ever), so there is very little improvement between the two pics, but they are over a year apart, just to note(latter was done first).
So, yeah, 'bout what I've got to say. Now rep me. ^_^