Be friendly and respectful and we'll notice. A big part of flirting with the waiter is simply not irritating the waiter. If you're at the bar during a busy night, you can earn important points if you drink your drink right away, order quickly, pay in cash, and leave room for the next customer. It seems counterintuitive not to prolong the interaction, but if you're an easy customer, he or she will remember you next time.
Being in a bar because you love the place and the people, not because they give you free stuff, will only make a waiter want you more. The best thing to do right now is to give up your seat at the bar to someone who keeps buying drinks (and, therefore, making money for your waiter). Bars make money with alcohol, so waiters can't serve you the bar just because you ask for it (or shout). Nowadays, many bars measure their drinks and even drink well, and asking the waiter to make the drink stronger, with a timid wink, is not a good idea.
