Start standing with your feet together, arms down by your sides. Take a wide step to the side with your left foot (your right leg should stay extended) and bend your left knee, pushing your hips behind you. Keep your back flat, eyes looking straight ahead, and reach both arms on either side of your left foot, touching the ground with your fingertips.
Push off the ground with your left foot, standing back up, as you cross your left leg over your right foot (think of stepping your left foot to the left corner of an imaginary box on the ground in front of you) and immediately bend your knees and reach both hands to the floor on either side of your left foot.
That's one rep. Quickly stand back up and push off your left foot, bringing it back out to your side and repeating the side lunge again. Do 15 reps on the right, then 15 reps on the left, repeating for a total of 3 sets on each leg.