What is the correct way to use the Zerostat?

Zerostats do not work. The problem is that as soon as the stylus starts rubbing the groove static electricity is generated pulling dust towards the record. There are two ways to deal with this. The first is always use a dust cover. If your table does not have one there are companies that will make one for you. You can hinge it to your cabinet.
Next is this  https://www.sleevecityusa.com/Antistatic-Record-Cleaning-Arm-p/tac-01.htm. I have used one version or another of this for 40 years. The bristles of this arm are conductive and its base is connected to ground. It dutifully follows the grove discharging the static and sweeping any incidental dust out of the way. If you have a good mat and a record weight you will not hear it at all. At the end of the side I give it a wipe with a standard felt record brush. I have never worn out a stylus .
You have to position the brush just right. Too close to the plater and it will skate inwards, too far and it will skate outwards. It should follow the record right along with the tonearm. It is terribly expensive at a whopping $20. As an aside, NEVER treat your records with any surface treatment. Last is a joke. It is just plain Freon! Nothing else in it. If you have some put a drop on a clean mirror and let it evaporate. Put another  drop in the same place and let it evaporate. You can do this a thousand times and you will not see a darn thing on that mirror. Nice scam. "Oh but it makes my records sound better!" Placebo. Anything that sticks to vinyl is going to gum up your stylus. The trick for keeping your records clean is don't let them get dirty in the first place. "oh but the record is loaded with all kinds of gunk from the factory!" My a--. Take a clean bright white cloth and spray it with a little distilled water. Wipe every new record you buy right out of the sleeve before you play it. Keep the cloth in a plastic bag. Wipe every new record you get for a year. What do you see on the cloth?
Anyone want to take a bet?  I do keep a Spin clean handy for when other people bring their records over or if I do something stupid like spill my coffee on the record.

Mijo, I apologize if it seems I follow you around here just to contradict you. That is not the case, and in fact I don't disagree with everything you wrote above.  But I do disagree with your bald statement that Zerostats do not work.  They can work, but most of us do not use them correctly OR, more often, we do something AFTER having treated the LP with the zerostat that puts a static charge back on to the LP surface.  There are long threads here (not this one) in which this is discussed in detail by others who have put more thought into it than I. But in the course of my own research on this subject, stimulated by one of the other threads here, I came upon a terrific white paper on static electricity authored by Shure.  Anyone interested in the subject should read it.

Second, I am not sure why you mandate use of a dust cover.  Dust is bad, but a dust cover is worse (than static electricity or dust collecting on the stylus tip) for sonics, when one is actually playing an LP.  In addition to the fact that a dust cover does not prevent the accumulation of a static charge and doesn't even perfectly solve the dust problem, dust covers cause a resonance and mechanical feedback that is very pernicious to SQ, in all my experience. As to the value of a DC for protecting the stylus from dust, there are quick and easy ways to clean the stylus even in between each playing of an LP (like Magic Eraser), if one is so inclined.  Further, taken by itself there is nothing to say about your claim never to have worn out a stylus; it's possibly true if you change styli or cartridges about every 500 hours, but it's not possible if you run one cartridge/stylus for many thousands of hours, dust or no dust. Anyway, my remarks are for a fun debate only; nothing personal.

Discwasher used with D4+ fluid is the best thing before using the ZeroStat. 

Lewm You can contradict me all you want.
Zerostats will kill static VERY temporarily. Like I said before the stylus rubbing the groove puts the charge back on in a hurry attracting dust to the record and there is plenty of dust in the air just look into the beam of a flashlight in a darkened room. The static and incidental dust are the reason you need a grounded sweep arm. It kills the static as it is being made. There is absolutely no downside to using a dust cover. They keep dust off the record and your delicate tonearm and they also decrease the decibels around your cartridge, arm and record. 
If you have a complex table like a Basis or VPI it makes keeping the table clean much easier. I would never use a table without one. The myths perpetrated against dust covers were generated by manufacturers who could not easily attach one to their table or by people who have no idea what they are talking about. When humans have no idea what is going on
they make stuff up. They mythologize.  Zeus throwing lightening bolts is a good example. The mythology surrounding Audio is second to none. I have fallen for it on several occasions. 

It seems you worship a different set of deities. I don’t and didn’t argue that a dust bug doesn’t work to reduce debris in the path of the stylus. And if you like dust covers, that’s fine too, but not for me and most others, when playing music.