Start by standing with your feet hip-width apart. Step your right foot into a front lunge. Check that your front and back leg are making 90-degree angles (aka that the knee is over the ankle, particularly of the front foot). Try to touch your back knee to the floor.
Drive through your front heel and propel your right foot back into a reverse lunge. Check that once again both legs are as close to a 90-degree angle as possible.
The key here is control; don't be in a rush to get anywhere!
Do this for 45 seconds, rest, then another 45 seconds.