I use the cross arm grip and think about looking directly up at the ceiling. Usually I wear a tank top but put on a t-shirt so the bar doesn#t slip on sweat. I don't look at the ceiling every rep though, maybe if I did I could do more. Usually stop when the bar drops too low on the way up.I've been supersetting mine with leg curls but I'm not even lifting any weight at the moment.
I've tried doing them using the cross armed grip but the bar always rolls off my shoulders making it very difficult to actually concentrate on the squats. I then switched to the clean grip and managed 5x8 at 60kg albeit painfully. I worked my way up to 75kg last Monday but had to stop after 3 reps on four occasions because my wrists were in agony.
Don't see much point in continuing with an exercise that causes me pain without working the body part I want it to. Think it's back to heavy leg press/zercher squats for me.