Hard to say what should be corrected. TFA has a shitty script but is nicely done on the surface.
If possible it would be cool to remove the inappropriate and unfunny humor (especially during Poe/Ren scenes), the ridiculous “fan service” elements (“oh, you’re General Han Solo !”, “12 parsecs” and stuff like that: it’s “Star Wars”, not “Last Action Hero”…), and most of “Jar Jar” Finn characterisation (this character is so stupid… why isn’t he killed ?). The same goes with the line establishing that stormtroopers are conditioned kids who hence don’t join the Empire by choice.
The scene with the space monsters aboard Han’s ship is so lame that it should be trimmed to basically nothing. Talking about Han, his terrible line “Chewie, we are home” is also something to definitely cut. Most of the really painful interaction between Leia and Han (has Lucas written those lines ?) must be trimmed.
There might be lots of other things but I must confess that I don’t quite remember a single scene free of lame elements in this (very) average movie. The Maz cantina thing, yep, also something to consider erasing (her “HAN SOLOOOOOOO” line… gosh, so lame…). Saddly it seems impossible to cut the terrible “Rey’s Jedi Mind Trick found in your magic pocket because the script needs you to use it now” scene. Close ups on General Hux during his speech (when he is almost crying like a little nazi doll) are to be removed as well. Most of Kylo Donald Duck Ren characterisation should also be removed in order to let the main villain look like a real threat and not a whining piece of shit kid who’s mad a his parents for grounding him.
ALL the opening crawl (the worst ever written in the saga so far) has to be rewritten to focus on the real heart and background of the movie: the Empire is back and going to strike harder than ever. Luke’s to be found should be only in the last paragraph, 'cause it starts the movie plot.
And at the near end, it would be better to wake up R2 before the script tells him to wake up (when Ren leaves the planet for instance ?), and to trim the shitty “let’s complete the puzzle map together” sequence so it wouldn’t look so dumb (well, it would still be a very dumb sequence anyway). The pathetic “National Geographic” final shot is to be put in a trash.
The deleted scene explaining the political background really needs to be reinstalled.
I guess it would end up being a 100/110 minutes movie, which is fine. It could be a good movie with those changes.
edit: the Han Solo/Kylo Ren scene should stay untouched. Even if the scene itself is lazy, there is a very beautiful direction idea with the lights getting down. The dialogue between Han and his son is also very good. Rey almost ruins everything with her “acting skills” in the aftermath, but Chewie going berserk is fine, so I guess it might be one of the very few good scenes that don’t need to be re-edited.