Hey there,
ok, i liked both the previous replies, they make sense and are actually good tips. But in my opinion, there are two more important factors here: BALLS and CREDIBILITY.
It might sound a bit harsh, but i dont intend any insult.
When you tear everything down, your thoughs/motives, you drink before sarging because you are afraid. Either afraid of approaching or afraid of not knowing what to say, or afraid of not being a fluent guy. In my opinion you lack the balls to go down crashing and burning

.
i am a very direct guy. I walk up to girls and tell them they are beautifull and drop dead sexy. Most girls have something like: is this guy for real? Some even ask me if i am drunk but i am always sober when i go out sarging. If i would be drunk while going in direct (or even indirect with flluff talk), you loose credibility. They are like: hehe yeah sure whatever, have another drink. But when i say to her: 'hey, i think you are absolutely stunning tonight and i want to see you again asap' and i am dead sober, she knows that i am well aware of what i am saying to her and that i am well aware of the possibility that she might (verbally) shoot me down in public.
Being drunk gives people a total different image of you. Imagine you walking down the street and one of your friends comes towards you. His eyes are fuzzy and he reeks like he swam in a pool of beer. He stands there next to you and say: 'dude, i just won the lottery and i am going to buy you a car because you are my best friend'. What will be your first thought? I dont think the first thought will be: ooh, i am his best friend! Neither will it be: show me the winning ticket!
Also, and lastly, being under influence while sarging also conveys a subtle message of insecurity and fear. You dont really want that. So if you are looking for motivation to not drink while or before sarging, perhaps it could be you trying to face whatever fear it is that makes you drink in the first place. Think about you becoming a stronger person.
cheers and good luck!