This is all good advice, but if you don't have any money or can't do it yourself, do what I did - "accidentally" destroy your walls. Get a lot of posters and hang them with the kind of adhesive that doesn't come off easily, and then in a couple weeks take them down. Glow-in-the-dark stars also work well for this. Also, knock a few small holes (tacks or nails work well) around the place, gradually peel back wallpaper, pick away paint chips, do whatever to make it look like your walls could use a good coat of paint. Even if you don't get the exact color you want you should still be able to influence it so that it's better than what you're stuck with now. You know how your parents are always nagging at you to keep your room clean? They'll be so embarrassed at your deteriorating walls they'll have to paint them!