Prep the Area
Clean and prep the floor. Cut lengths of tackless strip to fit each wall around the perimeter of the room. Secure them with the pre-driven nails into the subfloor, keeping the strip out from the wall about 2/3 the thickness of the carpet. Make sure the tackless strips join together at the corners and the pointed pins in each strip are facing the wall.
Note: If you are replacing carpet, pry up the old carpet from the tackless strip. The padding and tackless strips can be reused if they are still in good shape.