The following is from an article I did for the Illinois Bar Journal titled "Five Steps Towards Persuasive Writing." It's step two, maintain your credibility, and I was reminded of it this morning as I was outlining a memorandum in opposition to an opponent's motion:
The court will respond more favorably to your arguments if they think you are fair-minded and wise. The basic rules are easy. Present a cogent legal argument. Don't misstate the facts or the law. Be thorough in your research. Always cite-check your case citations.
Your credibility is also influenced by how seriously you take the arguments advanced by your opponent. Any legal brief or memo that fails to address every point made by the other side is inherently flawed. It's a rule that's often violated, especially when we're rushed.
What about concessions? It's often strategically wise—and an automatic credibility-booster—to state your opponent is right on points that don't matter to the end result. Why do so many lawyers feel compelled to defend indefensible positions that aren't material? Point out other reasons why you should win anyway.
Credibility also has a stylistic component. A common problem is overstatement, which will make the reader question every other forceful statement you make. Example: Defendant contends Smith v. Jones is distinguishable, but nothing could be further from the truth.
Never come on too strong.
You'll find the other four points in the linked article.