Before you purchase a hearth rug, find out what it's constructed of. Many area rugs marketed for use in front of your fireplace are not fire resistant and thus not suitable to be placed in front of a working fireplace.
Consider the price you want to pay for a hearth rug. You can find hearth rugs for very little money, or you can spend as much as you would for wall-to-wall carpeting if you have an unlimited budget.
Measure your fireplace so you can purchase a hearth rug that's large enough to provide you the protection you want. Take those measurements with you while you shop so you know what hearth rugs will work for you.
Take along colored photographs of your fireplace and the decor of the room so you can make sure the colors or patterns of hearth rugs you're considering will work for your home.
Estimate how often you use your fireplace and whether or not you use a fireplace screen. Select a hearth rug that's able to withstand the use you'll put it to and still be able to protect the flooring underneath.
Evaluate the hearth rugs. Hearth rugs made of fiberglass provide the most protection, followed by wool. Synthetic rugs melt very easily and offer little protection.