Oysters should be bought live, by law. Clamp them tightly shut. If they don't close immediately when touched, they are dead and need to be avoided. Smell them, too. If there's any kind of fishy scent, avoid them. Fresh oysters should smell like salted water. When buying them, make sure they are being kept in the store on crushed ice. Oysters should be stored in a container without a tight-fitting lid. Put the top half of the shell down, and cover with a damp towel. Store in the fridge for up to a week before serving. Use oyster knife blades; a stainless steel blade is preferred, to shuck your oysters gently. Scrub off any dirt or debris from the shells. Serve a raw oyster with a squeeze of fresh lemon or cocktail sauce. Mignonette is optional.