My general advice for tantrums: ignore them, whenever possible.
You can explain how 'everyone gets a turn to be first' when he is NOT upset, not in a situation where he is frustrated and angry. He *really cannot hear you* when he's angry. Lord knows-- I worked with kids long enough and what I have come away with is that they can hear us before and after a tantrum, but not during. Their feelings are so huge, they lose all reason.
You might find a cooperative game, like Snail's Pace Race and focus on how the snails (or game pieces) each take turns being 'first'. No one is ever *always* first. (I like this game because everyone wins).
I also want to assure you that the small roadbumps in life are not an indicator that he's going to be shoving ahead of the line as a teen or adult, saying "M. first". He's still very little. When my young charges (as a nanny) or my son have a tantrum, we remove ourselves from the action (to room, back to the car, to a quiet place) and I just set them in a safe spot and say 'when you are ready to (wait in line, have the food... whatever), let M. know'. When they are done crying, I don't talk the subject to death, just remind them if need be, just "oh, I see the girl is using that right now. We can have our turn in a minute or go over to the swings"-- I give an alternative whenever possible but avoid trying to ensure that they get to be first...
... it's that old saying "you get what you get and you don't throw a fit". Of course, he's still little and might throw a fit, but then you remove him from the area and let him work through that on his own. Because you mentioned the attention piece (that the bigger the fuss, the more attention he gets), my strong suggestion is to keep removing him to a quiet place where he gets NO attention. No talking. No explaining. Just "Let M. know when you are ready to...." and then keep yourself busy, even if it means watching the squirrels at the park, pretending to read a book, noticing the signs in a driveway... whatever. No talking, no eye contact... eventually, there won't be a payoff for the behavior because no one else's world is stopping but his, if that makes any sense. And if the kiddos ever threw a fit in the library or a store, we left *immediately*. Throw a fit and the fun is pretty much over.