2. Poor posture
Bad posture can put extra stress on the back and shoulders, and also lead to a more stooped posture in old age. The Mayo Clinic recommends putting your chair at a height where you can rest both feet flat on the floor and keep your knees at the same level as your hip. You should also sit back in your chair and keep the top of your head stretched to the ceiling.
If you need a reminder, why not stick a Post-it note in a spot you’ll see it? Or try the Lumoback; it’s a device worn around the hips that vibrates when you slouch, reminding you to sit tall.