It's funny to think, but customers aren't just frequenting a bar because of the price of the beer. The general atmosphere has an impact, and indirectly the behaviour and attitude of the staff (preferably friendly).
How you approach bar work has a direct effect on how easy your night will go and how much you make in tips. It's just like life. Karma comes round, and if you mouth off at the customers it will come right back at you. Thankfully, my bar is very laid back, and usually if a bar person gives a customer some attitude, it's been deserved and we're usually backed up by management.
It's always wise in a busy bar to have a good sense of humour. It makes the shift go quicker and you'll enjoy yourself more. This relates to your colleagues and the customers. It's well known in our bar that the majority of the staff are bonkers (myself included). It's quite common for us to dance around the bar, juggle bottles/glasses and generally wind the customers up.
Personally, I think you have a be a flirt to be a good bar maid, and I will slyly wiggle my arse under the guise of dancing while fixing someone a drink. Makes me smile even if no-one else does!
Sometimes I even get a 10 pence tip.