Writing for the Legal Audience, by Wayne Schiess (Carolina Academic Press 2003), is a readable book with advice for lawyers writing for the following audiences, among others: the client, opposing counsel, the trial judge, and the appellate judge.
The publisher has provided an online file of the book's table of contents (pdf version). Amazon's information about the book is here. My post was suggested by a review of the book by Susan Wawrose in Trial magazine. (Sorry, no link available.)