If the service is good, I always tip well (20%+).
I tip more at certain places that I frequent often. For example, the place I get my hair cut, I usually tip 30%.
There was a bar that I would go to (recently just closed), and they knew me by face. I don't go out drinking often, but when I did, I would go there. They would take drinks off of my tab, and they would give me great service. In return, I tipped the bartenders nicely. It was a tradeoff. There are a few restauraunts that we go to often as well, and I tip them well; in return, they really take care of us when we come in.