Find a character system you like. For me, Its Disney. Im not an anime person, just never got into it, but I am a disney freak. second, learn to sew and find a costume maker. If your costumes has a loose seem though, you need to know how to fix it.
Third: Know makeup. Look up totorials on youtube. Im hooked on Mary Kay.
Forth: Believe in your self. Know that you CAN BECOME that character.
No matter what.