Hey Hamza, the first thing is your feet, so making sure you are on the balls of your feet (The front part near your toes). Focus on always staying low and keeping your head the same level when playing and switching. Then you need to make sure when playing your shots you are nice and stable so good solid feet on the ground so you can lean forwards and avoid coming upright and leaning backwards as you said.
Try some footwork drills when you are focusing on these areas and just go for consistency but really thinking about your feet and body position.
