It depends on what you like and how the rest of your room is decorated. You can do nature themes, a field full of flowers, the night sky, an ocean during a sunset, the forrest, etc. You can do a location theme, paris and the eiffle tower, disneyland castle, the great wall of china, etc. You can do a copy of your favorite work of art. You can do the walls like the inside of a tattoo parlor with flash art covering the wall....the possibilties are really endless.
things u like mybe fav animals.. it would be cool to have horses. or cheetahs lol