Well, I guess that depends how much time you've got and what kind of stuff you've got at your disposal.
Are you confident with a sewing machine? You could try taking the bodice off your dress and making a new one, so that you end up with something that's more of a typical 'prom dress' shape (i.e. the skirt sits on your natural waist). There's a tutorial with a pattern generator that might be useful, although I haven't tried it out: http://www.cutoutandkeep.net/projects/princess-seamed-bodice-pattern-generator
If you don't have a lot of time and/or you don't want to slash your dress to bits in case something goes wrong, you could try just adding some embellishments to it. See the band under the bodice? You could sew a new one over the top of it in an accent colour, or you could stick/sew on some sequins or other shiny stuff. You could try that on the actual bodice itself, although the pleats might make it a bit trickier.
Also, I've noticed that you've got some projects on your page using yo-yos and bows - why not make a bunch of them and sew them onto your dress? The picture in this tutorial is kind of what I mean: http://www.cutoutandkeep.net/projects/embellishing_a_dress
There are loads of tutorials on this site for making chiffon flowers and stuff if you'd rather do that. You could also make some for a hairband/some clips and coordinate your hair with your dress!
Another really easy (and cheap!) thing to do would be to whack some coloured tights on with it as well - worked for my prom dress :3
And one final, final thing - have you thought about making a dress from scratch? If your parents don't want to buy you a new dress because it's expensive then making one might work out cheaper. Make sure you leave enough time though (speaking from experience...)
Sorry it's such a long reply, I hope at least some of that is useful. You should totally post pictures after you're done as well :)