From my experience, since you even have to ask this question, the first step is desensitising yourself to the social pressure created by these situations. Instead of thinking how you can be comfortable striking up a conversation with that ONE girl, start from the ground-up becoming a social person who is comfortable meeting and bantering with all kinds of people you don't know, then when there's one girl you want to "make it work" with, you'll already be "in the zone" and you'll just start chatting without worrying about the "right thing" or not.

Don't know how else to explain it... getting good at game is often about shifting your reality, becoming familiar with situations and creating a sense of momentum and adventure, which took me a while to figure out. Early days were scary, paralysing in fact, but you see me day-gaming now and you'd think it's Neo from The Matrix who's can control his whole pick-up destiny (or at least believes he can). Think about the whole long-term process and how to become "that" kind of guy, and to cold-approach in any situation will become self-apparent.

By the way, who told you opinion openers were bad? I would be more situational and direct, but ANY leverage to "get your foot in the door" for experience is vital.