We suggest setting the pressure as low as you can while still allowing the post to fully return. You may need to adjust this over time as the seals and wipers 'wear in' or get dirty. A good range is 20-30psi for most ride conditions. Note: Don't rely on the gauge on your air pump. We have found that MOST pumps (even those made by reputable companies) are VERY inaccurate at low pressures. If the post is returning violently reduce the pressure or it may damage the post.
Note that when adding/removing air pressure from the Fall Line it takes approximately 5-10 seconds for the pressure to 'equalize' as air moves through our air cushion. If you are too hasty with removing the pump you will have set it at the wrong pressure.