Presets are relative to rider weight and style.
If you ride fast and hard and don't like the nose diving in corners or the soft feeling, or you might just be a larger fella, you'll need to go to a stiffer setting on the shocks.
If you are more of a Sunday slow rider, don't like a harsh ride, or are a small fella, you'll need to soften it up a bit.
As for the settings on the rear shock, it comes down to rebound (if it's adjustable) which has lots to do with rider weight. Bouncy in the rear, soften it up. Not quick enough to respond to the whoops, stiffen it up.
Nothing will tell you more than trial and error.
