Proper way to address a waiter or waitress
From what I have learned, the most proper and respectful is to use 服务员. There are many people that find 小姐 not appropriate or too traditional, I met several people who feel that 小姐 has some sexist note. The same goes for 美女 that many people use but not everyone feels comfortable to hear. 帅哥 for male 服务员 is less a problem as long as they are at the same age or younger and people definitely get served more quickly if they use this expression. After all you wouldn't use 美女 on somebody that is obviously older than you. Not to forget about the term 阿姨 that is a term of respect for a woman that is older than you, though not common in a restaurant, but you sure can use it in a small street noodle store (along with 叔叔 for male) where it can get more personal. I myself also often just use 你好 to address a service person.