As a former waitress, there are a lot of things that irritate me. I took pride in my job (it was my only source of income) and made TONS of money doing it before I became 'corporate'! I took my family to WDW/USF on that money I made there - and for two weeks at a time! Soooo....
First - ALWAYS stop by a new table to say "hi" introduce yourself, even if you're hands are full. Tell them you'll be right back. It's very appreciated.
ALWAYS give your name. I always liked when a guest would call me by my name, or go to the owner and compliment me by name, or ask for me again when they returned.
Drinks - start off with drink orders and quite possibly appetizers. Especially if it's super busy, ask the guests if they'd like an appetizer to hold them over. I always was honest and let them know if the kitchen was backed up or not. If no appetizers are ordered - bring out the bread! Especially if there are kids at the table. I hate sitting at a table with nothing in front of me (even water).
Know the menu - my boss always had us try everything. We tasted the specials every night so we knew what we were selling. I always let people know what my favorite was - they liked that, but you have to let them know if it's spicy or has mushrooms, or something else that they may not like.
Go back and check right after the first bite. After that - DON'T HOVER! I hate that - people want to eat, not have an audience while they do. I would usually do a couple walk-throughs without bothering anyone. It makes it look like you are checking, without actually 'checking'.
EMPTY THE ASHTRAY!! ick! My boss said no more than 3 butts in the ashtray, and I lived by that. It's also a great way to check on drinks without the guest thinking that's what you're doing.
I'm sure I have plenty more! I'll post if I think of any.