don't forget, if your compression is jacked up then you might not be bouncing off the shock rebound but off the tires because you are failing to compress your suspension at all.
I start with everything open (no compression or rebound) then add a click of rebound until it's just past where i want it to be (it returns too slow) then I back it off a click. For compression, if your sag is set properly (air pressure) and you're crushing through your travel at a click or two of compression. if it starts to feel harsh, back it off a click. also, don't forget to set your sag (air pressure) with all your gear on and in the riding position you use most (for XC it's usually seated) and on level ground. to check your sag, sit on your bike a bounce a couple of times to cycle the shock, then have a friend move the O ring to the bottom of the slider and get off the bike gently. measure your sag.
Also, make sure your shock and fork aren't in climb mode. climb mode turns my 5010 into a hardtail instantly.