S-L-O-W-L-Y squeeze and then S-L-O-W-L-Y release, while aiming the gun at the LP and moving it around to cover the whole surface. If you hear/feel the Zerostat 'clicking', you're squeezing or releasing too fast.
correct zerostat technique
I have the Zerostat 3 and was always surprised at the lack of instruction supplied with it. I constantly wonder how to most effectively use it. In the past, a search of the archives turned up a tiangle technique. Basically, squeeze and release at the three points of an imaginary equilateral triangle ~1 foot over the record surface followed by one squeeze(no release) over the center. In max AC season here in Iowa this doesn't seem to be real effective and sometimes I wonder if I'm actually adding charge to the vinyl. Does anyone have a different technique to recommend? Would I have more luck with the Talisman or Furutech destat?(Both of which seem pricey)