Have confidence, user.
Easier said than done, sure. But once you can do this, everything becomes easier.
I used to be somewhat hesitant to talk to girls, but when you just say "fuck it" and go for it, everything works out. Turns out, women are happy to have someone to talk to.
Generally I just introduce myself and ask about their day. Already you've established that you're not a pussy like most of the other guys at the bar. Again, chicks dig confidence.
Hope that the girl doesn't have a bf (can be awkward to ask, so I usually don't). If she does, oh well, chances are you can meet her single friends.
Truthfully though, confidence isn't EVERYTHING. Of course other things matter. Being kind matters as well.
Failure to be friendly and polite will almost guarantee rejection. Don't fall for the "nice guy meme" meme.
Always ask yourself, "if some guy treated me this way, would I want them to be my gym bro". If not, you're treating her wrong.
Careful though, you don't want to get TOO fedora of course.
Eager-niceness is what I've taken to calling this...
For example complimenting her hair is good but don't immediately tell her how beautiful she is before even introducing yourself.
Remember this simple rule: "gymbro nice, not fedora nice". That should keep you from coming off as autistic.
Autism isn't something you should be worried about TOO much when talking to women though, otherwise you won't appear confident.
Me, I've basically followed these simple rules my whole life. I don't even work out much and eat lots of junk food like pizza, but I have no problem laying any attractive women I set my mind to.
Expect results to vary though. For of course, the MOST IMPORTANT features are spelled out at the beginning of each line. Failure to meet those basic requirements pretty much guarantees never exciting a woman, and dying a pathetic virgin.