Is there anything I need to read before Johns' Green Lantern

You need to read Emerald Dawn II (critical since it contains Sinestro's origin and sets the stage for Geoff's take on him), Emerald Twilight, Zero Hour, the first six issues of Kyle Rayner as Green Lantern (#51-55 and #0), Green Lantern #146-150 and Last Will and Testement of Hal Jordan (as these roll back the death of Killowag and the Guardians, plus introduce the concept of Ion), and Day of Judgement #1-5.

Also, when you start reading Geoff's GL run, around issue #10 IIRC (right when the "One Year Later" time skip happens) you need to read the 12 issue Ion mini-series (which has a plot point critical to Sinestro Corps War) and Infinite Crisis #1-7 and JLA #114-119.

Don't listen to this guy >>94752382 besides the Ion suggestion because it directly ties in. Stuff like Infinite Crisis gets recapped for you eventually. You don't need to actually read it even if it means things will resonate better emotionally later on. From experience, this was basically my first main comic run I read and I got it fine without having read any of that.

Honestly I think even Rebirth itself is debatable because it's mostly continuity cleanup and not very introductory. But the suggestion is Rebirth first then GLC Recharge, then you just kind of read GL and GLC ongoings until Sinestro Corps War where they crossover a bit. There are some spotlight issues to that so you'll generally want a list.