1. Everything has a place. Just take the extra 5 seconds to put things where they go and it will save you the hours of major cleaning up all at once.
2. Your room is not a Pottery Barn display. It may look great to have all your nail polishes on display, but is it practical? Always ask yourself that. Investing in pretty storage contraptions is a good choice, but I like using vintage suitcases (from thrift stores or Goodwill) to store things I'm not using at the time like winter clothes in summer, or vice versa.
3. Use your wall space. Feel bad throwing out birthday cards? Have a shoebox full of a bunch of magazine and newspaper clippings? Both save and show them off using cork, chalk, or magnetic bulletin boards.
4. You don't need paint to update your space. Need a cheap update? Try new curtains, rugs, sheets, or even photo frames to give a room a fresh feel without buying paint. You can even pay a visit to your local thrift shop or Goodwill store and find some interesting pieces of furniture and clean them up with that leftover paint or garnish that's been sitting in your garage for ages (sound familiar?).
5. Don't be afraid to throw out or give away. If you really and truly don't wear/use/like/need something just give it away or throw it out. Don't get attached to things that just take up your valuable space.