Need some advice, I’m a 26 year old dude having trouble figuring out how to actually initiate a hook up.

I’m actually in the following scenario very often and I’m about to be in it today again so I figured I’d try something new. I’m about to smoke some weed with a girl in my car and I know she thinks I’m attractive, problem is I usually just end up hanging out and talking instead of moving into anything sexual. How have you guys moved from the front seat to the back seat like what’s your game look like? What do you say