ditto what the others said.
best bet is quality premium points, and clean em with a piece of coarse paper.
filing them is for last resort.. as you quickly remove the hard surface coating. once you get into base metal.. they pit faster and you have to file more.
and don't even think about sanding them. sanding them leaves microscopic grit and scratches that encourage arcing even more.
clean with paper.. or move to a arid dry environment.