I would recommend working on your composition (Try placing your Text to the left or right a bit instead of straight in the middle) and your effects. I would recommend that you check out some of the beginner tutorial we have. Nice to see that you started up.
I’ll always remember the good times in my spine, and the holes I burned in my brain, with this next line.
I think it's a good try for a first one. Seeing as I was giving you some skills that weren't so...clear to the beginner-GFXer. I think that if you do some research (Or join GFX apprentice program) you'll get what you want soon enough.
Thats very good for your first sig. I would get out the sharpen tool and slighty sharpen some areas, that way it wont look as cloudy. Then I would burn and dodge some areas with a small circular brush to add some depth and contrast in the brightness.