The following is a brief overview of my opinion on how to properly hang prints.

Lighting:

This is the most important thing to consider when hanging a fine print, and also tends to be the component most often overlooked. Each print should be lit individually to avoid lighting up the wall. Excessively bright surroundings can close the iris of the eye limiting the viewer’s ability to fully appreciate the subtle tonal variations of a fine print. It may also strain the eye, making viewing an uncomfortable experience.

For the actual lighting, I prefer a low-voltage system. The primary advantage of these setups is the sheer variety of bulbs (generally of the MR16 variety). The bulbs must be carefully selected to correspond with the distance from the light to the print, the size of the print and the angle at which the light strikes the print. At approximately 6 ft from the print and a 35 degree angle off vertical, I find that a narrow flood (24 degrees) does well to cover frames 14x18 to 16x20. Bulbs should be selected to just cover the mat area, while not flooding the wall with too much light. A lighting expert will prove to be of great assistance in determining the exact bulbs specifications needed for a given situation.

One thing that all selected bulbs should have in common is the color temperature. This is essentially the color of the light in Kelvin. The lower the number, the warmer the color (yellows); the higher the number, the cooler the color (blues). I prefer a 4700 K bulb. It is very white, without going into the blue spectrum. If the ambient light in the viewing area is of a cooler temperature, then a bulb up to 5400 K may work well. To give you an idea of what this all means, here are some examples of approximate color temperatures:
A candle flame = 1850 K
Sunrise / sunset = 2000 K
A typical 100W incandescent bulb = 2865 K
Summer midday in the temperate region = 5400 K
Typical computer monitor = 9300 K

Wall Color:

Ansel Adams mentions that he most enjoyed his prints when viewed against walls with approximately 18% reflectance (middle gray), and specifically on one occasion when it was of a tan color. Most museums and galleries today use white walls. I have found white walls to be acceptable as long as the prints are properly lit (no excessive light falling on the walls) and the shade of white corresponds closely to the shade of the mat.

Print height and alignment:

Prints should be hung with the image center at average eye level, and it should be ensured that the lighting is not reflecting directly into the viewer's eyes. When hanging prints with different size frames many people often hang them by aligning the tops of the frames. But when I see prints hung this way, the first thing I think to myself is “nice hanging,” rather than “nice prints.” If instead the prints are hung with the image centers aligned, it emphasizes the image over the framing, and this should be the overall goal in hanging prints...

Emphasize the images!

A well done print hanging will be achieved only when the hanging itself goes unnoticed.