If a girl voluntarily agrees to spend time alone with you on a "date" then she's already viewing you as a potential sex partner.

So if there is a "method" then it is simply this ...

1) Don't do anything completely fucking dumb.
2) Ensure the opportunity exists.

RE 1, Just be your fun normal self, try to work in a bit of kino, don't be a pussy who fawns over her and agrees with everything she says.

RE 2, The best lines/routines etc in the world are not going to get you a shag if the basic logistics wont allow it e.g. your miles away from both your homes (or some other shag den) surrounded by strangers. So ensure the 2/3rd dates are at r near potential shag venues.