What you want to do is learn how to escalate properly. Escalation = moving a date (or whatever it is you're doing together with a girl) into the right (sexual) direction. There are 2 main ways to do it:
1) Touching - when you want to let a girl know what's up and move the date (or whatever) into a sexual phase, touch her more and start moving in closer as you talk. Make the physical aspect of the date more intimate.
2) Talking - you start moving your conversation into a more sexual direction. What you say really depends on the girl and your own confidence level. An example would be something like, "Wow, that dress looks really tight.. We should get you out of it as soon as possible
". It's a little weird if you escalate through talking with a straight face, you have to be flirty with it.
Both ways to escalate are difficult to explain, and sometimes the frame of a date will turn sexual on its own. But the best thing you can do is practice, practice, practice.
I had a huge escalation problem back in the day, and a friend told me: "Come on twice as hard as you think you should and scale back from there." That's exactly what I did. I went on about 5 dates where I held the girls' hands from start to finish and touched them constantly.. That's how long it took me to figure out what an acceptable level of touching is.
That's the most effective advice I can give you, too.
May the force be with you!