it's just my opinion and Phil is the obvious expert here, but I don't think you should use ANY pressure on the PC at first, just use the weight of the PC at first until you get used to it.
Oh, and if this is your first time with a PC, make sure you put the pad (loaded with product obviously) on the car before you turn the PC on or you're going to get yourself covered in wax/polish
Ask me how I know