Begin with your feet shoulder-width apart and your hands together at your heart. Note that this pose can also be done with the arms straight up in the air, but keeping the hands at your heart helps with balance.
Bend one knee, and use your hand to help prop your foot up on your standing leg.
When you feel stable enough, try lifting your hands straight up in the air for an extra challenge. You can also try closing your eyes because it will also challenge your balance even more.