Search the forum in the cyclocross section for more details, but the key really is to have the arms parallel with each other when the pads are touching the rims. Once you have the pads aligned properly, then you can work on the traverse length and main cable placement. In fact, I find that I can have the traverse cable any length once the pads placement is correct. This is going to sound obvious, but the key is to get the pads to make contact with with slight movement of the canti as it pivots.