What to wear?

Curl your hair & wear a shorter dress. Sorta flowy. But still hot.

You don't have to wear heels to go out clubbing, and you don't have to totally trade in your style either, unless you are going somewhere extremely fancy/expensive. If you aren't going somewhere super fancy, maybe just try to work from what you already have and are comfortable with to create an appropriate "evening" style. I really think nowadays girls can get away with wearing almost any individual piece no matter how casual, if they can dress it up properly. So if you have a pair of pants (or shorts or a skirt) you really like and fit you, you can actually use that piece as a starting point. If you team it up with dressier shoes - no, they do not have to be heels - great sandals or flats are fine too, and a simple but sexier-than-normal top. Really in the end, I think what makes it look more evening-appropriate is that normally it will look a bit more put together - that your hair is done more carefully, that you have a bit (or a bit more) make up on and that you add some accessories to make is look more dressy and complete. If you can give details as to your personal style maybe we could help you better!
As for me, I don't go out clubbing that much, more into cocktail lounges or sort of trendy bars, I would normally just go in sort of dressier (better fitting & darker) skinny-ish jeans, and a really simple sort of sexy black top. I do simple black pointy flats and just take care that my hair is a little more fixed than normal. I'm a strong believer in keeping it classy and not trashy (which I think is a mistake a lot of girls make). Chose one feature you want people to notice (ex. legs) and chose clothes/accessories that emphasize that (short skirt/short/shorts and heels/great flats) rather than go and try to emphasize everything/put everything on display (as in show of your chest, your back, your legs, etc, all at the same time) you will risk looking over the top and trashy. I'm kinda strange maybe, I like to think original, but I really just do the very simple, fitted almost semi-casual but still sexy outfit. Because I sort of have a very plain tall slimish body type I don't really over emphasize/ over sexualized it but rather sort of focus on the fact I find I have a really strong (sort of unique on women, think Angelina Jolie square-ish) jaw line, a long and skinny neck and very defined collar bone. To grab attention to that part of my body I got these insanely long earrings (seriously like 5inches) that sort of really stand out, shine and move a little. Its strange but those earrings, my evening out make-up, a simple bracelet and I've never been stopped anywhere even though the rest of my body is dressed the same as it would be any other day (well maybe the top is a tiny bit more fitted. All that to say, don't sacrifice your style entirely, don't make yourself feel uncomfortable, do dress it up a little and have fun. If you're still insecure about what to wear, talk to your friends about clothes and where you will go. I'm sure you'll be fine!