Sitting up straight begins with adopting a good, upright but relaxed posture. When you are sitting correctly, your feet will be flat on the ground and your knees will be a little lower than your hips. Ensure there is enough space between the seat of your chair and your knee (the width of four fingers or your fist).
It is also important to support your shoulders with the back rest. You are actually leaning back slightly. Bend your arms at a 90-degree angle and move your arm, rather than your hand, to operate the mouse. Last but not least, ensure your screen and keyboard are directly in front of you. The screen should ideally be at arm’s length, with the keyboard 15 centimetres from the edge of the desk.