The old Navy
way was to clean up the peeled up paint
off your steel deck
with a scraper. What doesn't come up with the scraper stays where it is. Prime only if all the paint is gone. Put on your first coat of paint (only where there is no non-skid), put down the sand with either the salt
shaker or the flour sifter before the paint dries. Let the paint dry then put on the second coat of paint.
I don't use a flour sifter or a salt
shaker. I do it by hand.
The more coats of paint you put on the less effective the non-skid. Sooner or later it will loose its non-skid qualities because you painted it too much and its time to remove it. Use a sharp scraper and peel it off or use the toughest grit concrete wheel
on your grinder and grind it off.
I've found this method to last 5 years before needing anything and you don't want to sit on it with a bare anything because you will get road rash. It is a very effective non-skid and doesn't cost much.