It might seem as simple as just going around and around but master the correct technique of the pedal stroke can help save energy and reduce your risk of injury.
Check Your Alignment
Ensure that your knee, hip and ankle are aligned directly above each pedal; think of your legs as pistons pumping up and down neatly and rhythmically. If you're not sure about your alignment then head to the gym and check your form on a spin bike by the mirror. Alternatively recruit a friend to film you whilst riding; that way not only can you critique the footage but you'll end up with a video diary so you can look back on your progress. Tip: Check that your knees aren't rolling in or out as you pedal.
Foot Position : Around the Clock Attention
Your foot position on the pedal and your heel height will determine which muscle groups you use to power you forward. Imagine the crank as the face of a clock and the pedal as the hour hand.
12 to 5 : The Power Phase.
During the power phase most cyclists lose power by not using their hamstrings. A simple fix to this problem is to drop your heel to engage your hammy. As your foot reaches 3 o'clock your foot should be parallel or even just a little bit lower through the heel.
6 o'clock : The Mud Scraper
The second phase is now to engage the calve muscles and drop the toes down to transition to the pullback phase. Greg LeMond best described this position as "like scraping mud off the bottom of your shoe"
7 o'clock : The Upstroke
A common mistake in this phase is to let the pedal do the work and push the foot up. Engaging your quads and hamstrings to pull the pedal up from 6 - 12 will give you maximum power. As you approach 12 don't forget to prepare for the power phase and repeat the process.
Take note of which muscles ache after your ride and be conscious of your technique for maximum pedal power!