Hey dude,
I remember asking myself those questions once too. What works good with me to transition into the more sexual vibe and sexual talk is really more body language and facial expression. Theres a point where it doesn't really matter what you're saying as long as your saying it slowly or having pauses, stronger eye contact , flirty facial expression (evil smile). practice in front of a mirror first.
If you really want to have some sort of technique you can always use you could try this it worked great for me the other night.
So your having a good friendly convo. and your teasing her and building a friendly social connection. If you teased her a good amount your most likely have higher value at this point so you could go right ahead and give her a compliment to let her know you are interested in her. BUT! right after that you make her live up to that compliment and prove it to you. like this :
YOU: Your eyes are very interestingly beautiful.
Hot babe: Oh, thank you

YOU: but beauty is so common, what would you say is something unique about you that other beautiful women dont have. what makes you special?
After that shell either start telling you, say i dont know, or say nothing im not to special. If she starts telling you she is now trying to win your approval, shes interested and you could forget about the friendly chat and start talking about hanging out alone together in the future. doing crazy things together. be creative.
If she says i dont know or nothing im not that special than she is insecure about her self and you have to lift her value a little more to be more comfortable with herself and with you. then you could try again with the same method but in a different way.
and as for those girls that say fuck off or any of that shit. dont take it personal. they get hit on all the time and are giving the quick bitch shield. Just move on and say "have a nice night". there are much better behaved girls out there. dont waste your time.
hope i helped. good luck