In Japan if you are in a restaurant and want the waiters attention, you can just yell すみません at the top of your voice and someone will come running. Now you probably know that translates to "excuse me" in English, but is it OK to just shout this in shops and restaurants in other countries? Well no, not really. If you are in a cafe or restaurant the most polite way to get a waiters attention is with eye contact and a raised hand. Saying "excuse me" in a loud voice sounds like you are angry. If you can't see a waiter (and I know this sounds strange) the best thing is to get up and look for one rather than just shouting. This might happen if the if it is a very quiet day or a very local area with few customers. If you really can't find any staff then it's OK to say "excuse me" and hope someone hears you, (this goes for shops too).