well, I guess some pretty basic tips that I can think of would be
1. ALWAYS get a wig! I don't care if your hair looks "somewhat" like the character or you think "you can just dye it and it'll be fine..."
2. try to be as specific with your cosplay costume as possible! if your buying a costume, make sure the company/seller has gotten good review!!
3. be IN CHARACTER as often as you can, sure there are moments when you just HAVE to squeel over that super cute axel that just walked by, but being in character can make your cosplay look a lot better.
4. PUT IN AN EFFORT! IT SHOWS!
yeah, that's pretty much the basics, but if there's anything specific you want tips or help with just met me know ^_^