Im a Ex legislator now, but served as the county executive for 1 term, the county chairman for one term, 2 council terms, 2 prom district terms, was the RW CA and write endlessly and drone on for the DOJ and private legal practice-
You learn from experience. I read a looooot of legislation, and took formatting ideas as well as wordings from other more experienced legislators.
Other then that, you learn over time. Its a learning curb if your not used to writing, let alone writing meticiously so that it satisfies both the purpose for the law and so that it is legally sound
Also, not to down on city/prom district attorneys, but a second opinion outside of them is usually a good idea. not saying theyre bad at their jobs but they usually miss things, and I speak from experience on that (Both as a former city attorney and reading stuff they passed when I was CE that was atrocious)