Paul,
I found this a usefull guide
http://www.flemingastrophotography.com/focusmax.html
Also make sure you set it to take at least 3 images per step to average out the seeing. Without this my curves were all over the place.
Although I must admit now days I am not using focusmax anymore as it was a bit of a headache sometimes with all those boxes popping up like crazy and the ascom nightmare.
Because I image using CCDsoft, I have found @focus2 to give very good repeatable results and its faster than focusmax.