A little fill flash would have given you some catchlights in the eyes , maybe a cooler fill, or some gel. Maybe a more relaxed pose, and a better background.
Apart from that I love the potential, your horizion is level enough and you've showed a considered disreagard for the rule of thirds.
When shooting a self portrait of yourself and new best friend (the camera), a flash in the mirror is going to be pretty bad. (This photo is not of me, by me, or for me)
20/05/2010 (Day 4.140) - Bad Self-Portrait by Kaptain Kobold, on Flickr
Pro tip: if you flip the image left to right, it's a little harder to tell it's a mirror photo. (and a cowboy hat helps with any portrait)
12234 by RexPhoto91, on Flickr