Talking to random people about anything, and talking to girls, and talking to girls romantically are all separate skills from talking to someone about an interest. I am going to assume you're a smart, educated guy with niche interests. So even if someone comes up and talks about something you don't know much about, maybe Biology for example (no clue if this is true), you are probably able to fill in the blanks, find a common interest, connect it with something you've re ad before or whatever. The real difficulty is when you then are talking to people without technical interests or such, do you fake talking about sports? Or whatever.
With girls, be up front, direct, don't shy away. Honestly a lot of the old PUA strategies work really well if you look at it like a skill you're building.
