The best position to work at a standing desk is with your feet flat on the ground, your knees slightly bent, and your hips in a neutral position. Your elbows should be at a 90-degree angle and close to your body, with your shoulders relaxed and not hunched up. Your monitor should be at eye level, and your keyboard and mouse should be at a height where your arms can rest comfortably at your sides.
It's also important to vary your standing posture throughout the day to avoid fatigue and strain on any one part of your body. Consider using an anti-fatigue mat to provide cushioning and support for your feet, and taking breaks to stretch and move around. Additionally, consider using a footrest or a stool to alternate between standing and sitting positions as needed.