Lung protection and eye protection. I used to work at a factory where these were used multiple times a day. Safety glasses were mandatory at all times. I would often watch and study my teammates getting away with grinding and cutting with just safety glasses. When I tried it, "ding"! Somehow that dang spec of metal would curve around the glasses and get me right in the dang eye!
I use safety glasses and a face shield when ever possible. Sometimes you get in a position where it's just not practical and you fog up, or can't see or fit into a small space, or upside down? And sometimes the dang dust mask won't work either and you gotta hold your breath?
I keep a cow magnet next to the bathroom sink. As soon as I get nailed, I keep my eye closed and head for the sink and retrieve the offending metal spec with the magnet before it has a chance to scratch my eye. Never did figure out what my teammates were doing differently?
Three types of discs to keep handy: skinny wheels, grinding wheel, and flapper discs. I have three grinders ready with each of those three wheels...