First you need to pick out a sickeningly bright or dark color. (Depending on your personality or something? I don't know. PICK A COLOR YOU LIKE.) I chose green. It's my favorite color. The actual swatch name was hilarious, and that's why I picked the color, but I can't for the life of me remember what it was. This is Awesomeosaurus modeling my headache-inducing color choice.
Collect cool items! -I- have a men's bathroom sign. I mean, how can you get cooler than that?
Gather your random nifty items. I'd take a picture of them in a pile, but it's already all up on my wall. So here, here is a picture of some of the stuff. What we have here is some paper ninja stars, some photos I took and cut up and made awesome (the buggie and Heather on the rainbow), a Village People record, the squid from a MSI album cover, star buttons/beads, Hello Kitty cut out a billion times, a Panyo Panyo Digi Charat poster, a unicorn, a Hello Kitty mint tin, a green lion named Freesh, a green lifesaver, a green apple. Haha. Yeah. Well anyway, go crazy. I attached everything with painter's tape because this is at my parent's house and I wont be here for much longer so I'll be able to take everything down and put it back up with ease.
Storage! I had this bookcase that was was just made of wood, so I went out and bought some black paint. The insides are painted with 1. The green I used for my room and 2. Acrylic paint I had left over haha.
Anyway, just make sure your room fits your style and really reflects you and what you're interested in. Make sure that everything you put up has a nice way of flowing together, or else it'll just look tacky. Happy decorating.