My most efficient bike pedal technique is to Push Forward with one foot pedal and Pull Back with the other foot Pedal simultaneously. When done right it feels like your feet are floating on the pedals. If your shoes are clipped to the pedal it makes it easier but you can still do this technique even without attaching your foot to the pedal but it's not as efficient and sometimes your foot slips off the pedal. So concentrate more on just pushing the pedal forward then pulling back.
As more power is needed I just push down more on the down stroke and or pull up more on the up stroke if I'm clipped to the pedal. Momentum is key so keep a constant speed peddle stroke.

. Bike Pedal Techniques Tutorial Video (Youtube)

I ride my bike, I roller skate, don't drive no car
Don't go too fast, but I go pretty far..Melanie Safka