How to hang art around a room. (see also my Board: Art: Displaying Art, for additional art gallery walls, and many more fabulous ways to display art. ~Alicia Stavropoulos) - A selection of interior design principals.
Hammer nail through a wooden ruler. Hang picture on that nail. Line it on the wall where you want it. Remove picture, push in nail to make an indent. Remove ruler, hammer another nail into the wall Hang your perfect picture up.