an easy way for people to think of it is this:
nose down = weight over front end = oversteer bias
nose up = weight over rear end = understeer bias
bump damping affects the suspension on the way down
rebound damping affects on the way up
so for more understeer bias under acceleration, you would reduce front rebound and rear bump.
for more oversteer bias while braking, reduce front bump and rear rebound.
All that said, the main point I am yet to really 'work out' is a good starting range. A lot of the time it seems that most traction under brakes and acceleration can be found with low damper settings. I've been running comparably stiff springs and quite low dampers for best times - this runs completely against any of the 'frequency' style of tuning that some have suggested in the past. On south city particularly, tuning for bump compliance gives much better cornering than tuning for outright peak traction.
Getting a handle on the dampers made heaps of difference to my ability to set up a car to suit me. Being able to adjust turn in under brakes, and behaviour under acceleration, mostly independant of each other is great. (Yes, this can also be done with the clutch pack dif)