In general I go in three-week waves, decreasing the number of sets. I can’t give you a hard and fast rule for sets and reps because it does depend on the individual, but a sample might be:
Unweighted: 12 x 3
2nd week (10% bw): 10 x 3
3rd week (20% bw): 8 x 3
As far as box height goes, part of the reason why I don’t do the same height for all of the sets is that often you don’t know exactly what you’re capable of.
So do a couple sets at a height that is “comfortable” (you know you can get) and start increasing it until you get nervous about missing it. Generally I’ve found that a good box height is one that you can get but makes you a little nervous, like you have to focus to get up there.