re: Does playing campaign mode of a FPS on hardest mode make you better online?

It helps a little, just for the fundamentals like accuracy, learning the controls, learning guns, etc. But like everyone else said, the AI can't simulate what people will do online, and you gotta learn the maps. Learning the maps is one of the biggest things, because no matter how good you are, you'll get destroyed if you don't know where you are or where you're going, where people like to hide, spawn points, etc. etc.