Because soft-shell clams don't close tightly like their hard-shell cousins, they might contain a little sand. To get them clean before cooking, place them in a large bowl and cover with salted water - 1/3 cup of salt per quart of water, dissolved.
A two to three hour soak should be adequate. Drain and rinse lightly under cold water.
Once the clams are cooked, handle them gently - they can fall out of the shells rather easily.