HQ Crafting, How does it work?

So I just got into crafting as most of my FC crafts and makes mil-gil doing it. I started with WVR and GSM. I know it really helps to have cross class skills but disregarding that, what is the deal with HQ crafting. Sometimes when I try to do HQ I will touch a few times get 60% and it'll be HQ and others it won't. Is there a general rule of thumb about how much you should use Touch until x% or is it completely random? I get everything else about crafting BUT quality control. Thanks!