Is this for tuning? Or just to see what #'s you put down?
I've been to a dyno enough and ran it enough and hell there is one ten feet from my office, so I've been aroudn them quite a bit.
I kind of have a checklist I go over. I check all the straps that they put on the car and make sure I can pretty much stand on them without them moving much. I check to make sure the car is centered well on the rollers, verify that the WB is reading correctly (if it's being used). Also one thing to make very sure is watch the Tach on the computer they have and rev the car a bit. Make sure that their tach movement is nice and smooth to indicate it is receiving a good solid signal. If you are driving it, go through the first 3 gears very easily, shifting at around 3k or so. Then when you get to 4th, let it bog down to about 2k, hit the green button, and go for it. It's a surreal experience to have the speedometer and tach reading what they are and to not be going anywhere. Have fun!