Wear the cleats around the house with the socks and shin guards you would use during an actual soccer game.
Put on the new shoes along with a pair of game socks, and soak your feet in a tub of warm water for 20 minutes. Remove your feet from the water and allow the cleats to shrink around your feet.
Take off the shoes and stuff them with newspaper, or put them on a shoe tree to retain their shape.
Rub the surface of the shoes with petroleum jelly to prevent cracking once the shoes have dried.