Variation 1: Side Angle Resting Arm
Take your stance one-leg width distance (shorter for more ease, wider for more challenge). Front foot with toes facing forward and back foot parallel to back of mat or toes turned inward 30 degrees. Have a strong lower body stance pulling inner thighs together and up towards pelvis to keep hips anchored with protuberances aiming perpendicular to front foot. Keep a long, lean torso (work that breathing to keep abs and back core engaged) lifting in a line coming off the back foot. The arm in the air lifts and continues the line from the back leg reaching up and past the head. The arm closer to the legs is merely light support for the torso with even fingers engaged as arm stays in shoulder socket. Look up to towards the sky/ceiling. This is Utthita Parsvakonasana.
Variation 2: Extended Side Angle
Same as Utthita Parsvakonasana above with exception of the arm that is closest to the legs. Without losing the length and lift of your torso extend the bent arm towards the ground and rest the hand or fingertips on the mat or a prop such as a brick placed on the inside of the foot. Keep the lifted extended arm going past the head to continue the line of the extended leg and torso. Rotate neck to look upward toward the ceiling. Ease off neck twisting if you have neck concerns, ease off the extended arm past the head if you have shoulder concerns.
Variation 3: Side Angle with Bind
Begin with the extended side angle with the arm resting on the thigh like in Variation 1 listed above. Get low into the bent knee so it is parallel to the floor and the knee is not past the ankle. Slightly rotate the torso at the waist and feel the extended arm fall away from the backside of the body. Release the bent arm and lower the shoulder of that arm deep towards the thigh of the bent leg as the arm that was on the thigh reaches under the thigh along the hamstring while the arm that was in the air winds back allowing pectoral girdle movement to glide around the shoulder blade and the arm reaches towards the hamstring of the bent leg. Allow fingers of both hands to interlace and breathe as you open the chest and allow the shoulder blades to play and give more room for the arm movement to make the bind easier. You can also grab a wrist with the opposite arm if interlacing fingers is too difficult to keep a steady breath in. This bound version of the extended side angle is also known as Baddha Utthita Parsvakonasana and is the preparation for the beautiful Bird of Paradise standing balancing pose.