Sources: Elements of Style is not enough
If you are a serious lawyer who cares about writing, The Elements of Style will take you only so far. It's a great book, written by a professor (Strunk) and his student (White) at Cornell--a superb institution with a tremendous law school and a beautiful campus "high above Cayuga's waters . . ." In fact, if you have a chance to read any book by a lawyer who went to Cornell, you should do it. Now.
Better Legal Writing
Writing for the Legal Audience
Anyway, back to Strunk & White, which will take you only so far. If you are serious about improving your legal writing, you'll need a serious guide. I recommend--
The Redbook: A Manual on Legal Style by Bryan A. Garner
It is a comprehensive guide to professional-level legal writing and will answer any question about correctness and style. The second edition will be out soon.