Small rooms can really make a wonderful space feel cramped, so in order to create the illusion of a larger room, you'll need to use a few crafty tricks to fool the eyes and brain. 

Many people who want to paint their small rooms think they don't have the option of using darker colors.  Go ahead and use those deep navy blues and dark olive greens, but instead of painting the wall floor to ceiling, only paint 3/4 of the way up.  Use a lighter version of the same color on the top.  This gives off the illusion the walls are higher than they really are and create the feeling of more room.

If you're looking for a good color to add more depth - go for cooler tones like blues and grays on walls.