A "technique" I use to test the waters is a simple upper back, shoulder, or arm rub.
Then I move to the lower back or legs (not inner legs tho unless it's obvious the girl is really into me) if the girl seems receptive
Then later I'll say "let me try something" and I go in for a kiss and then depending how receptive they are to that ...sex sometimes happens.

Or I don't say anything at all and just go for it if there's been enough build up.
edit: Also, timing for all of this could be spaced out by mere minutes, hours, or days depending on the girl.
[redacted] it was days (actually weeks...) because she didn't seem that into me until we were back at her place alone...
The new girl I'm currently with it was hours the first day we met and then we had sex the next day when we were alone together.