In The Curmudgeon's Guide to Practicing Law, Mark Herrmann, writing as a curmudgeon, states, "Any child can write a persuasive brief. Here's the magic formula. Follow it."
It turns out that the magic formula is short, easy to understand, and will work in most situations. Here's about half of it, taken directly from the book.
An introduction contains one or two short paragraphs. It has no footnotes. It says something sexy about the case.
II. Allegations of The Complaint (in a motion to dismiss) or
Undisputed Facts (in a summary judgment motion) or
Facts (for most other briefs).
In short sentences, bring the reader up to speed. Include in your statement of facts every fact that you will later mention in your argument. Do not include facts that are unnecessary for your argument.
Our client is entitled to win for [three] reasons. First, [reason one]. Second, [reason two]. Third, [reason three].
The rest of the magic formula includes advice for organizing each of the argument sections and drafting part IV, the conclusion. I stopped short of quoting the entire formula here, but if you want to read it, it's in the book's first chapter, which you can read for free on the publisher's website. It's titled "How to Write: A Memorandum from a Curmudgeon."
The publisher's website also includes the book's foreword and the table of contents. Be sure to take a look. Since I first posted about The Curmudgeon's Guide to Practicing Law in April, I've read the entire thing. It's easy to recommend, especially for litigation associates at large defense firms. All types of lawyers will benefit from reading the book's first chapter.