First, make sure your pad is at least as large as the rug. It can be slightly larger, but not too much bigger as dealers sell pads by the square foot size. Next, position the pad exactly where you want the rug to lay. Then place the rug over the pad. Grab a pair of really sharp scissors and carefully trim the pad all around so that the rug is about 2″ larger than the pad on all sides. Be sure that the edges of the rug touch the floor, but don’t leave too much excess rug. If you have too much excess you run the risk of creating a place where the rug may slide.