The Calf Raise is a great exercise to improve your lower leg muscles for two reasons. It both increases your cadence by allowing you to twirl the pedals more quickly and gives you more power by increasing your push off the pedals at the top and bottom of your pedal motion.
To do calf raises, first position your toes on a raised bar that allows your heels to drop several inches below your toes. A curb or set of stairs will work just fine for this. You can hold dumbbells in your hands if you want, or do this with no external weights.
Slowly raise yourself on tip-toe, and then allow yourself to sink back down to where your heels are as far below your toes as you can go. You will feel a nice stretch in the back of your calf. Then raise yourself back up to tip-toe and repeat. Do three sets of this, with 15 times each time.
Most weight machines have a station that allows you to do calf raises with weights. This is usually where you would perform the shoulder press or bench press workout. To do calf raises with the machine, instead of lifting the weight bar over your head, simply hold it chest high or down by your hips if it is already on a lower setting, and work the calf muscles by raising yourself up and down on your toes. Oftentimes there will be a raised set that is intended to be used with this, which allows for you to work the calf muscles through their entire range of motion.
You can also do calf raises in a seated position at the machine, or else simply by using dumbbells and a step as shown in the accompanying photo.