You never ever say Fräulein. It is disrespectful. 100 years ago it was a normal term to refer to an unmarried woman, but today it is rude, almost insulting. Please don't use that word, ever. It's Frau Müller for a woman and Herr Müller for a man, regardless of age and marital status.

If you want the waiter's attention, make eye contact, and give a nod or a subtle hand gesture. If they are obviously busy then wait.

Here we treat waiters mostly as equals. Imagine it as if an acquaintance or a neighbour was serving you - that's much closer to how you should treat them.