The pile of a carpet is the "visible surface of carpet consisting of yarn tufts in loop and/or cut configuration," according to The Carpet and Rug Institute. A carpet's pile can become flat, losing its plushness, simply from heavy traffic, heavy furniture and a lack of raising it on a regular basis. The carpet tufts actually get smashed down into the air space between them. You can revitalize pile carpet and make it look like new again as long as it's not terribly worn or damaged.
Run a vacuum sweeper across a pile carpet weekly to help raise it as well as to remove dirt and debris. The carpet will last longer. Vacuum against the direction of the pile to suck up more dirt and stand the pile up.
Place carpet casters underneath furniture legs to help raise pile carpet. You can also move each piece of furniture an inch or so in any direction every week. That way, the legs won't be in the same position all the time and crush the carpet fibers.
Run the flat edge of a ruler or a credit card across the fibers to raise pile carpet. Plug a steam iron in and set the heat on "Medium." Hold the iron approximately 3 inches over the pile for a few minutes. Allow the carpet to dry thoroughly before you walk on it or place anything on it.