Tons of ways you can introduce sex talk - I just look for opportunities, usually with frames or jokes that have an underlying sexual tone.
I like sexual humor because it's two-fold; it builds rapport and eases her into feeling comfortable with you AND, because of the sexual undertone, it gets her to feel comfortable talking about sex/thinking about sex.
Also, this really depends on which style of game you have and what will be congruent with your personality. I'm fun and laid back while maintaining being direct so sexual humor suits me well but I have some friends who are more monotone/serious/apathetic who cannot pull off the same humor, as me.
Her: "Yeah, I've had a really long day of work! Stuck behind a computer screen all day."
Me: "So, what you're really telling me is you've been watching porn all day." <-- Computer screen
or
Me: "Oh, really? You know what the best way to de-stress after a long day is?" *wink and smile*
Her: "What's that?" (usually she'll smile or play with her hair because she picks up on the sexuality"
Me: "Ice cream! Let's go!" *Purposefully denies confirming her assumption that you were being sexual*
Keep in mind that I utilize a lot of sexual frames while doing daygame. If you're on a date and sitting down face-to-face then you can actually have direct sex talk where you open about your experiences and she does the same - this one happens a lot more naturally because women will typically ask you about yourself and you'll have several opportunities to relate it to sex.
The overarching point here is that you, yourself, need to be comfortable talking about sex because it's no big deal. If you show any nerve or uncertainty about it then it will creep her out.
-Richard
