Although not commonly used with pranayama, the standing position can be used when doing pranayama and is useful if lying down or sitting are not possible for whatever reason.
Start by standing with your feet about a shoulder-width apart. Feet should be parallel.
Bring your awareness up from your feet to your pelvis and make yourself aware of where the centre of gravity is. Gently move your pelvis forward/backward/sideways to feel where the centre point is. Your weight should go directly through the centre of your body.
Let the arms hang naturally, and the same with the shoulders.
Bring your awareness up to the neck and head. Your head should balance on the neck and not feel like it is leaning forward, back or to either side. You can imagine a piece of thread extending from the crown up to the sky, gently lifting the head (keep the chin parallel to floor).
Keep the eye gentle fixed on a point directly in front.
Now you should be in a relaxed standing position with your weight finely balanced. Little effort is needed if the weight is correctly placed through the centre of the body. Imagine a plum line going through the centre of the whole body, with the body balancing on a centre point.
Now the body is relaxed and balanced, you can start pranayama.