There's only one 'Star Wars' movie you actually need to re-watch before you see 'The Force Awakens'
There's good news:
You actually don't need to watch any of them before you go see J.J. Abrams' "Star Wars: The Force Awakens."
The movie does a good job of explaining itself to even the least knowledgable "Star Wars" fan.
But! If you want to be let in on some of the inside jokes in Abrams' movie - because he does include a fair amount of throwback references for the avid fan's viewing pleasure - there's one movie you really should re-watch above all the others: "Episode IV: A New Hope."
"A New Hope" was the first "Star Wars" movie George Lucas ever made. It introduces you to everyone you'll need to know about in "The Force Awakens," including Luke Skywalker, Princess Leia, Han Solo, and Darth Vader - even Chewbacca, the wookiee.
There are a lot of similarities between the two movies, too, both in terms of plot and in cinematography. For example, there's a famous bar/cantina scene in "A New Hope" that Abrams recreates in his own vision in "The Force Awakens." And there's a famous trash-compactor scene in "A New Hope" that Han Solo jokes about in Abrams' new movie.
Anyway, if you're not up for binge-watching half a day's worth of "Star Wars," just go watch the very first "Star Wars" again, and you won't miss much at all.