I haven't really figured it out.
So far, I've gotten best results by relaxing and getting my mind into a calm, meditative state, focused on the present here and now. Each rep is the ONLY rep there is, and you do it, and then the next rep is the same, and so on.
I know it sounds a bit hokey, but it's helped with the 20 rep squats. My biggest problem with it is I have to consciously make sure I keep up a decent pace. I tend to do my reps too slow and get worn down from the bar on my shoulders.
Hyping myself up for sets that take awhile, time-wise, doesn't seem to do any good.
The anticipation is killer though. Some of the sessions I've dreaded for awhile. I'll let it build up, and then get annoyed... and then actually just go do it.
(Also, 165 for 50 reps in as few as sets as possible... why?)