Vasisthasana: Identify the critical elements of the asana

To first get into this asana, you must be Tadasana. Place your toes at the front of your mat with all toe mounts pressing into the ground. Lift your arms using your breath, slowly bring them down and reach the use the tips of your fingers to touch the mat. Inhale, exhale lengthen, keeping your legs straight. If you are unable to keep your legs straight while reaching to the ground, then slightly bend the knees. Now with your hands, create the same foundation as you did with your feet, by pressing all the fingers to the ground. Now that you have reached Tadasana with your hands, jump back into your plank. Engage the legs. Now what happened to your hands? Are they still in Tadasana? Yes they are, still maintain Tadasana within your hands and lift those knees into the quadriceps.
Now that you are in your plank, slowly now begin to rotate the right foot so that the outside of your right foot is on the ground. Your feet now should be in Tadasana by pressing the toe mounts into that imaginary wall. With you left foot, lay it on top your right leg as your body is on your right side. If you are unable to maintain balance, you can use your left leg to keep you up. Bring your left leg over the body so that your left foot is now pressing into the ground, creating a L shape.
By keeping a good foundation in your legs, now begin to open up the chest by pulling the ribs outward. Pretend there is a wall behind you and try to get your back as parallel to that wall as possible. Using your left arm, reach towards the ceiling so that you get the entire alignment.
To get out of this pose, use your breath. Inhale to bring the left leg back on top the right leg and exhale to rotate your entire body back into the plank (original position.) Now do the left side of this pose by repeating all the steps above using the opposite.