Thanks, Manny. You know how hard it is to type those lengthly responses with one hand??
Compression: A lot of folks think that the less the compression dampening the better. Manny delt with this, so avoid the clunk. Work to find the balance.
Shock Rebound: Shock rebound is hard to set, as rebound that is too slow can cause "packing", making the rebound feel too fast. With packing, your shock is rebounding so slow that it does not have time to rebound fully before you hit the next bump. The result is that it "feels like" you shock is rebounding too fast. Most folks will turn the rebound adjustment screw in a few more clicks, making the packing even worse. If it feels as though you have too much rebound, or like the shock is kicking you in the rear, it is a good idea to turn the srew out as an initial test to see if your shock is packing (keep notes, with comments, as you might find the best ride early, but then not remember what it was by the end of the day). If you are starting fresh, start with the adjustment screw in the middle and work out or in. My shocks (stock and revalved by ACME) usually settle in at around 10 clicks out from full in, but I hate too much rebound because I ride so far over the bars. Also, when turning the adjustment screw in all the way, be careful not to bottom the screw too hard against the seat, as you will distort the seat. It takes some practice to dial in a shock, but just practice. Use an experienced rider to help by watching you hit the whoops or jumps. Your freind will be able to watch the bikes balance as you pound the whoops, with invaluable input.
Fork Rebound: Fork rebound is much less critical than shock rebound, but a well tuned fork can mean the difference between suspension that works pretty good, and suspension that works great. In general, forks that rebound too slow will rob you of the initial dampening characteristics of your compression circuit because the forks never have a chance to return to full extension. (As a note, I run my rebound faster for woods riding and slower for desert and high speed riding. In the woods, you rarely bottom the forks, and want to be able to get around the turns at every tree. Keeping the forks fully extended helps keep the weight balanced between the front and back.) Start your adjustments by setting the rebound screw in the middle, and work the compression adjustment first. Once compression is pretty close, turn the rebound screw in or out (does not matter at first) three turns. Ask yourself if the result is better or worse. If rebound is too fast, you will deflect rather easily, so turn it back to center and then three turns out. Too slow, and you lose some suspension travel. This is essentially trial and error. As a general rule, my fork rebound will be plus or minus no more than three clicks from center. Just remember, as you change fork compression, you will have to change rebound.
Finally, don't try and perform initial suspension testing by just going on a ride. Instead, find a section of trail with turns, whoops, jumps, etc. and ride it until you are comfortable, then begin to change suspension settings. Fine tuning can be done later, but initial tuning should be done a the same section over and over and over and over...
If you are having a tough time setting rebound, post up your questions and we'll try and make things work out.
Good luck.
Rick