Very Particular is a gear perk that slightly raises your damage against tagged enemies. Since you will tag most enemies anyway, it is a small but steady damage boost.
Shots against tagged enemies do a little more damage. Tag with your camera or a tagging perk first.
Wear the Kyrati Gloves in the hands slot. Gear perks are fixed to the piece of clothing that carries them, so you get this one by wearing that piece, not by unlocking it in a menu.
Tagging perks such as Tactical Awareness or Takedown Tagger mark more enemies for you.