concentrate on sweeping your feet backward at the bottom of the stroke. Sort of like shuffling your feet backward on the floor.

on the upstroke, think of trying to pull your feet out of the pedal by pulling up.

At the top of the stroke, think of pushing your feet forward.

and where you normally mash. concentrate on just relaxing.

If you have a trainer, fluid or mag doesn't really matter, do the one legged exercise with the resting feet not clipped in. try to get your pedals to spin evenly. On a trainer you really don't have to think about where you are going or stopping so you can just concentrate on the spin.

Out on the road, ride on a lower gear and spin more instead of mashing.

And there is always a true fixie. Make sure you get a bike with a front brake. Now that will teach you to spin whether you like it or not. There is no coasting.