I think being pushy or aggressive towards a shy girl in the early stage doesn't work.
Base on my experience, I have encountered a lot of shy girls. What works the best is to really talk to them and listen to what they have to say but before you start building rapport, ALWAYS turn on your attraction button. Being confident and funny are also consider attractive as well. Also try to tease her playfully but not too much. From here, observe her body language and indicators of interest. The indicators that I always look for are making sure she's contributing to the conversation, she tells you about herself and try to continue the conversation. If she does this then she is interested in you then slowly move into the rapport stage. If she doesn't show any indicators of interest then just move on dude. Plenty of girls out there but if she's into you. This is where you get to know her well and most importantly MAKE HER TALK. The more she talks then the MORE comfortable she will be around you. Sometime you just gonna ask question that makes her think deeply. For example, I met this girl and I asked her question like "What kind of guys are you into? Do you like guys that have look or guys with good personality?" You see here that you make her think. If she answered "I'm into guys with personalities" then you can ask what kind of personality traits you like the most?" It really doesn't matter what her answer is. The thing is to make her talk and feel comfortable. When you know her well then slowly move into the seduction stage then you should know what to do from here.
I don't pick up girls from bar/club. Those are not quality girls. Just imagine, how great can they be if they just out hunting for sex?