You can stand with your back braced against a wall if you feel unsteady in this pose.
Deepen the Pose
As with Tadasana , you can challenge your balance by practicing this pose with your eyes closed. Learn to balance without any reference to the outer environment.
If your raised foot tends to slide down the inner standing thigh, put a folded sticky mat between the raised-foot sole and the standing inner thigh.
Benefits
Strengthens thighs, calves, ankles, and spine
Stretches the groins and inner thighs, chest and shoulders
Improves sense of balance
Relieves sciatica and reduces flat feet
Partnering
If you are practicing Vrksasana with arms raised overhead, a partner can help you lift and lengthen your arms. First raise your arms perpendicular to the floor. Have your partner stand behind you and press inward against your outer upper arms, then lift your outer arms toward the ceiling. At the same time, draw your inner arms downward, from the wrists to the tops of the shoulders.
Variations
Stretch your arms straight up toward the ceiling, parallel to each other, palms facing, or touch the palms together forming an inverted V with the arms.