Discovered this by accident awhile back and it works like a charm. Make a date with a girl, then call and cancel the day of. Has to be something that came up and is important, but not exactly something that makes you have to cancel.
Be apologetic and polite but cancel and ask to get together another time. Its tough to do especially if you like the girl, but it will pay dividends. They will start thinking about you and get really aroused and wonder what your story is.