Persistence...

Sometimes you'll knock on a door and nobody will answer. Sometimes you'll do it again and nobody will answer. Sometimes it takes a few times until somebody opens the door. It's a lot like that when it comes to looking for gigs -- sometimes you get ignored for a while before you get an answer, whether it's yes or no. Remember, a club will get along just fine regardless of whether or not they book your band; you're not even on their radar, so don't think that they're in any kind of rush to have you play their club.
But you have to keep knocking -- keep following up until you either get hired or they tell you to stop bothering them. And no matter if it's the first time or the forty-seventh time, you have to do it with a smile -- or at least keep it polite and professional.
And if you ever, at any time, act like an ass while you're doing this, club owners and managers will always remember that you're an ass.