I had 2 servers last week who committed 3 faux pas that I don't easily forgive.
1. Don't ever interrupt a conversation at the table except to tell me there's a fire in the kitchen and the exit is to my left.
2. Always know what beers are available on tap, what beers are available in bottles and what today's specials are. Be clear and specific if asked to describe a dish.
3. Don't ever take the check after I've placed currency on top of it and ask if I'll be wanting any change. I'll probably change my mind if you do.