When it comes to Halloween, you try your best to be original. You look at store bought costumes, and you even try to think of something to put together by yourself. It seems you end up never really knowing what to wear. See what your personality suggests!
Steps
If you have a big interest, such as acting, be a movie star. Or if you love sports, you could take it one step further and dress up as Derek Jeter or Tom Brady.
You could always pick something simple, such as a fairy-princess (think glam accessories, glitter, makeup and pink) or an animal of any sort (think a certain dominant color and a few accessories).
Simply dressing up as a classic sort of thing (witch, cheerleader, etc.) can get boring after a while, so instead, put a spin on classic costumes! You could "halloweenorize" them by making it a goth cheerleader or a goth witch, or even have a preppy witch!
If you really enjoy making costumes and spending a lot of time on them, do something really elaborate and unique. Examples: Evil fairy, Jellicle Cat, various anime characters, any mascot-type costume. Only do this if you're really serious about it, though.
If you really like to shock people a bit though, why not go in the total opposite of what you are, sure it would be hard to keep up, but what is one little trip to the other side of the fence? For example, a prep dresses as a goth, a boy dresses up as a girl, or a popular person dresses as a geek.
Tips
Be creative! You can never go wrong with a creative, all-your-own Halloween costume.
Buy costumes cheaply for next year just after Halloween
Add a special touch. Carry a prop associated with your character.
Act your character. Are you muscular, sexy, old, creaky, zombied? That should tell you how to talk, walk move etc.
Dress Apropriately. That naughty nun outfit might be a hit at the local frat house, not so much at the Methodist Fall Festival.
Warnings
Try not to stretch it TOO MUCH, or, on the other hand, do something TOO cliche. Honestly, who really needs ANOTHER witch??
Don't go too crazy if you can't pull it off. It might be funny for some guy to go as a playboy bunny as a joke, but others might not be able to pull it off.
The best costume is one which anyone can recognise, but no-one has thought of. Be imaginative, but not too obscure.
Be sure that cars can see you when crossing the street. If your costume is all black or mostly black, make sure to put reflective tape somewhere on your costume (chest, head, shoulders, arms, somewhere that a car driver can see you).