@chinski

well you need to watch Prometheus first because its a sequel to it and there is many references to it as well as characters..

have you even seen the first 2 (essentials) 2 movies of the serie? Alien, then Aliens?

the 2 others sequels of Alien, like Alien 3 and Alien: resurrection doesnt matter at all for the serie, they are still good watch but you have to see Alien, Aliens then Prometheus in order to understand and hopefully appreciate Alien: Covevant at the bets you can because there is a story Arc between those 4..