In the Bikram Yoga posture sequence, all standing postures start in the Anatomical Position, which I call, Start Position. Basically, it's just standing upright, facing forward, with your feet together and arms resting naturally by your sides.
Some Western yoga traditions use the strict medical version of this posture, which has the arms turned outwards to face the palms forward, but in Bikram Yoga we use a more relaxed version.
We also keep the feet together but this isn't an absolute, as there are many situations where it may be appropriate to have some space between them.
While in Start Position, always keep your attention focused on your body and breath. Pay particular attention to the muscular action of standing still with an erect spine. Keep the weight evenly distributed throughout the feet. Gently contract the muscles of the feet, legs, hips, lower abdomen and buttocks to fully support your spine and upper body. Relax the muscles of the face and neck. Use just enough shoulder muscle contraction to keep the shoulders in line with each other and not sagging, or dropping forward.
Breathe slowly, gently and deeply, with a steady rhythm of inhales and exhales. When you notice your mind wandering just let the intruding thoughs fade away and come back to your body. Intentional breathing like this should be maintained as much as possible throughout your practice.
The strongest postures, including Start Position, use firm yet gentle muscle contraction. Too much tension anywhere in your body can inhibit the benefits of your practice.