Give it some rest - first stage for 1 to 3 months (depending on how bad it is) - dont do any bent over rows, seated cable rows, squats, leg press (unless they are partials), rear lateral raises (unless you are lying on a bench), or even heavy dumbell presses or shrugs or anthing where you have to yank heavy dumbells or pick them up from the rack - you get the idea, anything where your back is bent over with weight interferes with the rest stage. A typical back workout can be: lat pulldowns or chinups, hammer strength rows (since you chest is resting against a pad), followed by t-bar rows (the kind where your chest is pressed against a pad too, and dumbell pullovers. None of these exercises put much strain on your lower back.
After a little while start to do hyperextensions and/or light weight on the lower back machine where yous it and push a pad backwards which rests on your upper back and start light deadlifts like 135 to 225 lbs.
Listen to your body, when when you think you're ready more or less go back to your normal workouts, but probably still do hack squats (or even front squats) instead of traditional squats, deadlift a bit lighter than usual but with more strict form and higher reps, etc.
And always stretch it, practically every time you are in the gym.
