I'm definitely NO expert,... so I spoke to my Kawasaki mechanic, and he told me that most factory bikes are set with their suspensions in the middle settings - ie, turn the Preload all the way to the softest setting, then count either the "clicks" or number of turns, all the way through until the limit (hardest setting), then calculate the "midline" - usually 2 and a half clicks from either limit.
The other options are to start from the softest settings, and work up.
Or measure the bike sag, G-sag, etc (see other thread re suspension settings).
Hope this helps.
Dr Dan