Ardha Chandrasana is often performed as an extension of the posture Utthita Trikonasana. My procedure steps are going to assume that you are starting in this way.
Steps:
1. Start in
Utthita Trikonasana on the right side.
2. Place your left hand on your left hip and use it to rotate your hip to make sure that your heart's center remains open. Inhale, slightly bending your right knee, and slide your left foot between about six and twelve inches closer to your right foot. At the same time, slide your right hand forwards at least a foot, keeping it to the right of your right pinky toe.
3. Next, straighten your right leg and arm, pressing them firmly into the ground, creating a strong foundation to help you maintain your balance in this pose. This action should cause your left leg to rise up until it is parallel to the ground and in line with the rest of your body. Keep your head in line with your spine, do not let it hang.
4. Stack your left hip above your right hip. Flex your left foot. Activate both of your legs by lifting the quadriceps, making sure that your right kneecap hasn't rotated inward. It should remain in line with the second toe of your right foot. Keeping both legs strong is very important in this pose.
5. If unsteady, keep your left hand placed on your hip. If balanced, raise the left arm straight up in the air, in line with the right arm, and turn your gaze to look up at your fingertips. Keep the heart's center open and remain in the position for between thirty seconds and one minute.
6. Repeat on the other side.