Try to make your stroke smooth and round. Also, try to spin at a high RPM and see how fast you can spin. So if you are cruising along at, say, 20 mph, drop down a couple of gears and see if you can maintain speed at the higher RPM without bobbing on your saddle. As your stroke becomes smoother and more efficient your ability to spin smoothly will increase. This will make you more efficient overall. As they say, RPM=efficiency.