simple laser level
hammer nails/screws (depending on the weight of your artwork)
Depending on on wether you own the artwork already, or if you are planing to purchase artwork the following steps can be used either way. If you are planing to beautify that wall over you couch or bed using masking tape to outline what looks proportionate is very helpful.
If you already have the artwork and want to make sure it hangs just perfect use masking tape to outline the position on your wall. Play with the outline to get ideas of how it will look when you walk into the room or how the light will interact with your art.
Once you establish your favorite spot you can use the masking tape to hang the works precisely. With two inch masking tape you have enough room to eyeball the overall position and then measure and mark the final nail/screw spot. In my sample pictures I am hanging a group of 9 minis square 8"x 8" frames. I laid the frames out on the floor as a square to get a feel of the best spacing between the frames. Then I measured the length and hight of that layout. Using a tape measure I cut the masking tape to length.
(If you are not centering your art ignore the next step.) To center my work I measure the length of the wall. After deducting the the length of my horizontal tape outline from the length of the wall measurement, I divide the resulting figure and establish the starting point of my outline. To make sure my first and most important line (the upper masking tape line) is level I measure the tape line on either end from the floor If the floor is not level use a simple suction cup laser level. ($20 at Home Depot/Lowes/ACE/neighborhood hardware store) Use the laser level also to insure that the vertical tape lines are perpendicular to your upper tape line. You can use your horizontal bottom tape line to verify that your layout is square (or rectangular depending on your art work).
After finishing my outline I step back to make sure I like the hight and overall position. Turning two frames still laid out on the floor on their backs I measure the space between their centers (hanging points). Using that measurement I mark the centers of the frames onto my top masking tape. Now I run masking tape vertically along those center marks (use your laser level again to ensure squareness). Applying the same measurements that I used horizontally, I mark the vertical spacing (this being a square layout).
Having nine marks for nine frames I drive my nails through the tape marks. Pull the tape off with nails in place. I hang the frames and enjoy my new artwork.
artwork at moderneditions.com
the laser level from home depot has an electric vacuum pump that uses suction and will not damage the wall