It's not a mechanical thing in order of status. Numerous other things come into play, including party size, special meal requests, seat assignments, and check-in order.

There was a rumour in the past that where a passenger does something especially helpful on a flight, the senior cabin crew member has a facility to log it against their customer record on the iPad which will result in the passenger being prioritised for an upgrade at the next opportunity. I have no idea how true this is.