For me it's:
-push upper back against bar
Doubly hard at my sticking point. If I do these, everything else takes care of itself.
Different people sometimes respond differently to the same cue for the same problem. What works best for me is figuring out what might be wrong technically, then figure out the best cue to fix that.
My biggest technical weakness in squats is letting my knees drift backwards too soon and letting my hips shoot up and the above cues snuff that in a hurry for me.