Could someone explain preload and compression damping?

[Brammofan]

I was looking at the "Suspension" page of the Wiki because I am considering adjusting what I can to make my ride less jarring.  The two adjustments available on the Brammo Enertia are:
1. Preload
2. Compression Damping.
Preload is adjusted by turning a ring next to the spring on the Elka rear shock, and damping is adjusted by turning the knob on the top of the rear shock.

What should I fiddle with first, and which direction?  Also, if I adjust the preload, should I just use an adjustable pliers with some sort of rubber protection on in to avoid scratching the ring?  Or is there some official tool I need to buy for this one function?

[Gavin]

i would wait for a Saturday or Sunday and then go to the place you feel that your ride is "jarring". Then it is just a matter of  "many runs" over that same area...

only make one adjustment to the preload at a time. then put that adjustment back and adjust the opposite way. then put that back and adjust the Damping. and then the opposite way. then adjust the preload in the direction you liked best AND adjust the damping in the way you liked best...record that mentally and then adjust the preload one more step...record that again and adjust the damping more...keeping going back and forth till you find the best ride "for you"

trial and error is a bit of a pain, but lots of time on your bike is a pleasure, so they balance out.

Gavin