A large pea sized blob should be enough, get a nice even thick layer over each pad, but avoid any skin creases at the joints, or else you'll be asking for a split. Leave it for 45 minutes, wash it off. You won't notice much until about two days later.
I don't reckon you should use this stuff more than twice a week though. I don't bother with it much these days, not much use for grit, especially winter grit, but still good for indoors.
I've heard some people leave it on overnight, but not sure this adds anything over the 45 minutes - god help you if you rub your eye in the night. It would be interesting to hear exactly what amputees do with it . . .