Approach with confidence.
Confidence is one of the most desired traits of a man. When you have targeted a specific woman at a bar, do not wait for her to talk to you, as the probability of this happening is low. Instead, approach her directly and with confidence. This means walking with a confident posture and eye contact.
Begin the interaction non-stereotypically.
For many, the purpose of a bar is to meet potential partners. Being so, the woman you are approaching has likely been approached several times. Do not use pickup lines. Do not compliment her looks. Do not ask her personal questions. Say something interesting and creative or ask a question that is likely to yield a more-than-one-word answer.
Continue the conversation while simultaneously implicitly displaying your positive traits.
The topic of the conversation is not important, as meaningful communication in romantic pursuits is mostly nonverbal. Talk louder than you feel is necessary; remember you are in a noisy bar and likely to be misheard. Displaying your positive traits includes showing kindness and compassion, comfort with being close to women and intellect.
Move out of the bar.
Take the woman outside, whether to another venue, a restaurant or your home. Do not suggest to move from the bar, but actually make the decision. In other words, do not ask if she would like to go with you somewhere but state you and her are going elsewhere and take her there. If you were successful in your interaction with her, it is unlikely she will refuse. Congratulations, you are now on a date.