The biggest trick I've found so far is to change my mindset from "this button casts this spell" into "press this button when this happens". For example, my "spam" button will cast a spell from the mage and /castsequence dots from the warlock. The real trick is to get the timing of the spells the same. If one is casting a 1.5 second cast an another is casting a 2 second cast then you won't be as efficient unless you are really spamming the button .