It is rude to snap your fingers or clap to get the waiter’s attention. The usual approach is to catch the server’s eye and then raise your hand slightly to indicate you need something. If the waiter is nearby, but not looking in your direction, it is permissible to call “Waiter” quietly, but not so loud as to be heard around the restaurant. If your server is out of sight, you can say to another waiter or waitress, “Excuse me. Would you please call our waiter?”