I haven't written a diversity statement myself, so I'm no expert; however, I think it should (ideally) indicate that the candidate has considered their own identity; the relationship between their discipline and minoritized communities; and the steps they can take--in research, teaching, etc.--to foster meaningful inclusion. Unfortunately, I don't have any tips, but I think they're popular enough (esp. in job applications) that you can find online resources if you haven't already taken a look.