I suggest reading a PUA book like Revelations (the only one worth reading, as it is more about what you want in your life than getting girls) to answer your question.
Making the conversation interesting is your job, not hers. Doing this is a skill like any other. Personally I think just going up to someone and start a conversation is rather lame and too direct. Find a reason to stand nearby and drop a short comment that makes her want to reply. Go from there. See a nice girl on a bus stop? "Pretty cold these days, isnt it?" Stuff like that also helps if you are a passive person, as it will not come off as fake.
Once you are in the conversation, you need to stir it towards a conversation you desire, not hope she starts a good topic on her own. And dont expect a drunken slut you want to bone to sound intelligent in a club, even if she is smart. As long as you keep the conversation interesting AND control where it goes... its in your hand if its good or not. And if she is not on your level at all, feel free to drop her.
Also as long as you dont have the aura of Saidin, you prolly dont get many girls walk up to you and start a conversation because you look all cool standing around over there. You need to start the conversation, yet make it casual like you didnt intend to, but enjoy her company more then whatever else you were doing a moment ago.