Couple tips. Start by thinking of each stroke section separately. Pushing down through the front is easy, followed by pulling back slightly at the bottom (think of wiping your shoe soles off), then think unweight your foot as your coming up the back side, and as you round near the top of the stroke pretend your going to throw your knees over the handlebars (helps carry momentum forward). The coach at my shop suggested concentrating on each stroke section independently for about 30 seconds each, alternating through all four. After you get the feel of each section, start blending them together.

It really just comes with time, and a cadence sensor helps. If you've got a trainer or rollers, now's a good time to work on stroke. I just started road riding 4 years ago and could barely hold 60-70. Worked all that first winter on cadence and now average 95-105 consistently.