Mirrors help...something well placed and tasteful.
Can you post a picture of the room Grace. There are many tricks, mirrors as Lori suggested, also using a monochromatic light color scheme, and/or textures instead of prints, but a photo of the room might help us come up with more ideas for your room personally.
Lighter colors tend to feel more open as well.
less is more :-)
Accessories can be big help in a small room, but the biggest secret is to select the right size and amount of furniture. Its intended use is also important. If it is a guest room, all you need is comfort for a guest for a short time. If it is a kid's room, you will need storage and milk crates as shown in an earlier post today can be used in strategic areas. A kid will need junk storage space so a smaller chest with a stack of crates attached to the wall might serve better than a large chest! Good luck!