what is the best exercise/stretching/posture that will separate the vertebrae of the spine? I want to do this because I read that separating the vertebrae will allow the compressed intervertebral discs to decompress/swell again, good if you are sitting too much.
There are several ways to decompress your discs and spine. The first is prevention by minimizing prolonged positioning, especially poor sitting posture. This q/a gives you several ideas, as well as stretching and strengthening exercises to improve your sitting posture.
To decompress your spine and reduce the effects of gravity and prolonged sitting you can do traction, stretches, massage or learn to open and close your joints with Tai Chi or Yoga.
You are wise to address your spine as part of your overall fitness. Set up a daily routine to take good care of your spine on a regular basis.