If you want to be able to hold your body up in an arm balance, you have to have a strong upper body and core. This pose will strengthen both.
Come into a plank position with straight arms and legs. Make sure your shoulders are stacked over your wrists. Bend your left knee and squeeze it into your chest. Hold here for five breaths, step your left leg back, and bring your right knee forward. Repeat one or two more times. Your arms and abs should be feeling worked after a few reps.