Hello! To start out, you could look around these forums and figure out what con you're going to, weather you'll buy/commission or make the cosplay, things like that!
As for suggestions, you'd make a great Ms. Marvel, Ty Lee, Asami Sato, Belle from Beauty and the Beast, Terra from Teen Titans. I hope I gave you some ideas! Good luck!
Next Convention: Anime Detour
Ino Yamanaka- Naruto Stage Play Live
Mistress 9- Sailor Moon