How should I sit to avoid back pain?

How should I sit to avoid back pain?
When seated, keep these tips in mind:

Adjust the height of your chair so that your feet rest flat on the floor or on a footrest.
Keep your knees at or below the level of your hips.
Adjust your chair to support your back or place a rolled towel or small pillow behind your lower back.

When seated, keep these tips in mind:
  1. Adjust the height of your chair so that your feet rest flat on the floor or on a footrest.
  2. Keep your knees at or below the level of your hips.
  3. Adjust your chair to support your back or place a rolled towel or small pillow behind your lower back.