A mix of sizes can make art difficult to space out. (onurdongel/Getty Images/iStockphoto)

Hanging light fixtures, flat-screen televisions and art all require commitment — you've got to put holes in your walls or ceiling, which can be a scary proposition. Design clients and friends come to me all the time, paralyzed by the thought of getting it wrong. The right measurements depend on your physical height and the room's use, but there are guidelines you can follow. Here's how to make sure your walls don't end up looking like Swiss cheese.

Artwork

The biggest mistake people make when it comes to hanging artwork is not hanging it at all. David Kassel, the owner of ILevel, a professional art installer in New York, says that people are just too scared to put holes in their walls. But unlike a light fixture or flat-screen television, hanging art does very little damage to your wall (the thin nails used in hanging most pictures make tiny holes, and if you mess up, the picture usually ends up covering the hole).

As for art placement, Kassel says there is no right or wrong, but there are some general rules of thumb: When hanging art, make sure you consider the room's purpose. In a living room, for example, art should be hung at a height that looks good when viewed while standing and sitting, but in a hallway where you are always standing, you might hang pictures a bit higher.

In general, pictures should be hung so that the center of the work is at eye level; for most people, that means the middle of the picture should be about 58 to 60 inches from the floor. Kassel says adults often automatically hang pictures at an adult's height in a kid's room, but it's better to hang it at a height that suits the child.

When hanging pictures next to one another in a grid, you should have about two inches between items (both vertically and horizontally). If you have a grouping of different-size frames that you are hanging together, making even spacing difficult, Kassel says to keep a minimum of two inches between items; it will give the grouping visual cohesion.

Flat-screen televisions

Most professional television installers will tell you that many people ignore the optimal height guidelines for hanging flat-screen televisions because they choose to hang their televisions over a fireplace (which is almost always too high). Optimal viewing, no matter the size of your screen, is straight on at eye level. Travis Bingler, commercial account manager at the Charlottesville-based electronics store Crutchfield, suggests always assessing the right height from a seated position rather than standing, and whatever you do, make sure you have thought of all the installation logistics — the wires, power source, components and cables. "For many," he says, "the guts of the TV are an afterthought to the placement, and they can't be."

Sconces

If you hang wall sconces too far apart, your room will look disjointed — but too close together and it will look cramped. When hanging sconces in a hallway or living space, you want about eight to 10 feet between the fixtures so that they emit a good balance of light. As for their height, they should be just above eye level, anywhere from 60 to 68 inches from the floor to the center of the sconce back plate. Sconces on either side of a bathroom mirror should also be hung just above eye level. When hanging sconces on either side of a fireplace, consider the mantel width. If your fireplace is very wide, they should be hung over both ends of the mantel, not way off to the side. Near smaller fireplaces, sconces should be about eight inches from the sides of the opening.

Dining room lights

One mistake people make when hanging their dining room fixture is that they hang it too close to the ceiling, giving it no relation to the table.

You want to center the fixture over your table and hang it so that the measurement from the bottom of the fixture to the surface of your dining table is between 30 and 36 inches. Also, choose a fixture that has a width at least six inches narrower than the width of the table (on all sides). If you are like me and you move your dining table from time to time for parties, use an S-hook on the chain to lift the fixture up five or six notches to accommodate people walking under it.

Wall-mounted reading lamps

The best way to establish the proper height for wall-mounted lamps is to sit on your sofa or lie on your bed as you would when reading and measure from the floor to just above your shoulder. You want the fixture mounted so that the light hits between your head and your book. For couples of different heights, it's best to pick a mounting height that is a compromise of the two measurements. In general, the top of the fixture should be about 55 to 60 inches from the floor. As for width, I suggest mounting the fixtures about eight inches from the sides of the headboard.

Mayhew, a "Today" show style expert and former magazine editor, is the author of "Flip! for Decorating."