Bring things you only absolutely need for school. Pack them up in a footlocker or chest that can fit under your bed or at the foot of it. Include clothing that can be worn now instead of for the whole year. Bring a few small things that remind you of home that won't take up a lot of space, such as pictures and your own bedding. Raise your bed's height by placing cinder blocks or wood blocks under each post-- this will make room to store more underneath it.
Store clothing and books in colorful, stackable crates for better organization. This will leave your belongings in the open while still being neat and tidy. Take CDs and DVDs out of their cases and put them in a carrying binder specially designed for these media types. Put all your bath and body items in decorative storage boxes that can be stacked and displayed your dresser or desk.
Use wall hooks and over-the-door hooks to hang up jackets, hoodies, scarves and robes. Most wall hooks are easily installed and taken off without damage to the walls.
Use a compartment shelf that is made for hanging up in your closet. These contain three or four shelves and hang from your closet rod to maximize space without taking up much of it. They also come in a few different sizes for shoes, clothes and heavier items.
Hang a bulletin board up above your desk to keep your homework due dates, special occasions and other important dates on hand. Get a lamp that has more than one use, such as charging your MP3 player and holding pens and pencils while giving off light to reduce desk clutter. Get a file folder expander to store important papers so they don't get lost or misplaced.