Step your right leg wide to the left, coming into a lateral lunge, bending your right knee. Keep your chest lifted and your weight in your right heel.
Push off with your right foot, and cross the right leg behind your left, coming into a curtsy squat, bending both knees. This completes one rep.
Step out to the right, returning to your side lunge; continue alternating between these two moves for a total of 12 reps. Then repeat on the other side.
This is a great exercise for working your glutes from all angles.