If you didn't spend your childhood balancing books on your head in charm school, your posture may be less than ideal. Slumping over a keyboard with shoulders hunched can cause chronic aches and pains.
Good posture requires some conscious effort at first, but then it's second nature!
At a desk. Keep your back pressed firmly against the chair, knees level with or higher than hips, feet resting on the floor.
On a couch. Keep a small pillow behind your lower back.
Standing. Give your back a rest by placing one foot on a low stepstool or an open cabinet.
In bed. Sleep on your side with a pillow between your knees, or on your back with one beneath them.