Bartenders remember good tippers/nice people. Don't think if you throw a bartender a five, you can act like a total jack *** and expect to get great service.
If it's a busy bar/club kind of place, a dollar a drink is fine. If it's a slower bar/restaurant/etc. and they'll be able to remember you, throw down a nice tip and if you frequent the place often, it should come back around to you.