Sit with back straight, buttocks touching the back of the chair, shoulders over hips.
Use a chair with lumbar support, or use a towel or lumbar cushion.
Adjust the chair so your legs bend at a 90-degree angle.
If possible, use an ergonomic keyboard to keep your wrists in a straight, neutral position.
Tilt the monitor so you can look straight ahead at it during the day.
Take breaks to stretch and walk around every 30 minutes.