Have you rehabbed your back? Or have you just not used it since? There may (or may not, depending) be certain rehab exercises you should do before getting back into deadlifting, so consulting with a sports physio would be a good idea, unless you already have the green light to start deadlifting. Once you're at a point where you can safely deadlift, it's really quite obvious - start light, progressively increase weight in very small doses. Even if you only increase your working weight by 5lb/session and start at a weight that you could currently barbell row, that will accumulate over time. Obviously make good technique a priority, and it might be wise to avoid going to failure, given the nature of the injury.