Hello! Being a cosplayer that has had braces, I know how you feel. Braces are something you can't help, but they will not make your cosplay look bad! If you feel self-conscious about it though, you simply don't have to smile with your teeth. As much as braces are a bummer, in the end you'll have very pretty teeth and many years of braces-less cosplay ahead.
In Progress: Syaoran: Tsubasa Reservoir Chronicles/ Yusuke Urameshi (Dark Tournament): Yu Yu Hakusho/ Yoh (Revamp): Shaman King/ Jenos Hazard: Black Cat/ Teito Klein (Mourning Robes): 07-Ghost/ Kaito Sinbad: KKJ