This thoracic-opening exercise can make a big difference in your hunched-over posture. It promotes extension in the thoracic spine, which is usually hunched or rounded forward in flexion with kyphosis.
- Stand facing a table or counter that's about waist to chest high. Place your hands on it and walk your feet back so that your feet are under your hips.
- Look at your feet and make sure they're straight or even slightly pigeon-toed or turned inward (this is really important). Kick your buttocks/hips back to place an arch in your lower back and move your chest down towards the floor. Keep your elbows locked out and tighten your quads.
- Breathe and hold for 1 minute. Make sure to keep the weight distribution in your feet equal.
- Repeat daily.
You'll need more than one stretch of course to fix poor posture, but this is a good start. See the related links below for more info.