Measure and mark a grip pad to the same dimensions as the rug. If you're concerned that the pad may stick out past the edges of the rug, you can take 1 inch off the length and width of the grip pad.
Cut the grip pad to the measured size. Any pair of scissors should be capable of cutting through the pad.
Lay the grip pad down on the floor in the spot you intend to put the rug.
Stick heavy duty double-sided tape along the edges of the grip pad. This tape will help keep the rug in place as well as prevent it from curling up in the corners.
Lay the rug down on the grip pad. If possible, have somebody assist you to ensure you get the placement right on the first try. It may be troublesome to remove the rug from the taped pad if you don't get it right the first time.
Press down along the edges of the rug to fasten it to the grip pad.