(i) Press down. This is what all riders do. No need to elaborate.
(ii) Lift on the upstroke. You can experiment to slightly lift your foot on each upstroke. Your foot may still on the peddle but the weight of your leg on the upstroke peddle is reduced. You should feel the difference immediately that you move faster without pressing down harder. This lifting of your foot uses different leg muscles from those to press down. You may feel your tired muscles when you do this repeatedly. After keeping doing this for a while, you can strengthen those muscles.
(iii) Move your feet in a circle. When you combine your regular downstrokes and newly practiced upstrokes, you can imagine that your feet are not going down and up but moving in a circle following the peddles. If you can do this, you are in the rank of professionals. This is what they do in Tour de France and other races.
(iv) Pull your upstroke foot. This is similar to (ii) but you intentionally pull up your feet on upstrokes. You can’t do this without toe clips or cleats. This can also be combined with (i) to form the circular peddling motion of (iii).
(v) Push by the heels. You can lower your heel on each downstroke and push forward using your heel instead of press down using your forefoot. This again uses different muscles from those for pressing down. Similar to (ii), you would feel tired on those muscles first, but with some training, you would strengthen them. This works well for me especially on climbing.
(vi) Stand up. This is a good skill to have for two reasons. First, on a long-distance ride, you need to release the pressure on your butt to prevent or mitigate saddle sore (see this article). Second, on climbing, you can use the weight of your whole body to peddle down. This would tire your leggs more quickly and should be used only when you know the road will be flat soon. The worst is you peddle by standing up and find out you have yet a long way to do on the uphill.
(vii) Peddle with a high cadence. This is a common practice of pro cyclists. Its major benefit is to reduce stress to knees and use a different type of muscle fiber from those when peddling with a low cadence. When your first try high-cadence peddling, you may feel tired quickly. After some practice and training, you will get used to it. Then you peddle with high and low cadences in rotation, you’d delay your leg fatigue. Another benefit of high-cadence peddling is to shift some burden from your legs to heart. At a given speed, high-cadence peddling would raise your heartbeat rate faster than low-cadence peddling. A healthy heart should return its beat from high to normal rates very quickly, within a few minutes, during a short rest. When you feel tired in your legs, it takes much longer to recover, probably overnight. How high is high? Higher than you feel comfortable now until you reach > 80 RPM or higher.
All these peddling skills allow you to use different muscles of your legs. When you rotate them on a long ride, your legs would thank you.
Chidong Zhang's WA2MA Bike Trip 