Start by picking through your clams to discard any that are open or chipped. Place the clams in a bowl, then add fresh water to cover. Let the clams sit in the water for 20 minutes. This will allow the clams to expel any sand that may be in their shells. These days, most clams are farmed and typically do not contain much, if any sand. Drain the water, then scrub the clams with a soft brush. At this point, the clams are ready to cook.