As long as you are good in balance this exercise is very simple and it's an exercise that you can do anywhere. You just have to stand in one foot only and go up and down using your leg muscles. Alternate your legs as they are feeling sore and do the most repetitions you can.
Details: Don't arch too much and don't stretch your legs too much because bigger movements makes you come out of the tension zone to the comfort zone and that makes the exercise less effective. Stand completely straight to keep your balance so you don't have to stop during the exercise to go back to the balance position. Plus, if you stand straight you can prevent spine problems.