I used to work at a pretty nice family owned Italian restaraunt. All I did was bussed tables but working there I learned a lot from the servers. They expect tips to be above 15% no matter what, and they prefer 20%. Some have even said that anything below 20% is a 'bad tip'. So regardless whenever I go out to eat as long as I have enough money I always try and tip at least 20% unless the service was particularly shitty. These servers don't make a lot of money and most of what they do make comes from tips. Plus it makes you look like a pimp if you spend lots of money lol.