1. Focus primarily on repeating the arguments of your favored party. After all, anything worth saying once is worth being said by everyone who wants to say it. The official term for this (originally from Law French) is the "moi aussi principle."Eugene, of course, is humorously describing common problems with amicus curiae briefs. As the person resonsible for drafting CAC's amicus briefs, I have seen all of these foibles many times over. Here at CAC, we try to avoid making these mistakes, though admittedly we're not always successful. Our brief in the Michigan affirmative action cases was largely repetitive of the general arguments offered--but then again, with more than 90 amicus briefs filed, it's hard to say anything original. At least we kept our brief to eight pages, likely making CAC's contribution to that case the shortest of the 90-plus participants.
2. If you do have a genuinely original twist to add to the analysis, don't just stick with it -- that's bad form. Be sure to surround it with lots of other points that echo what your favored party says (see item 1 above). A ratio of 10 page of repetition to 1 page of new material is the norm, though experts believe that even this is too low.
3. Always include lots of general rhetoric, such as "The importance of the timeless guarantees of the First Amendment cannot be overstated in our marketplace of ideas, and the republic on which it rests." Judges and law clerks just love that sort of stuff. This is especially true when filing briefs before the Supreme Court. The sorts of close and difficult cases that the Court hears are almost always decided primarily by applying general slogans. In fact, it's considered disrespectful of the Court to focus on mere factual details, or to use more mundane language.
4. Always keep in mind that (according to Rule 3.7), "The primary purpose of an inimicus curiae brief is to allow the inimicus to tell donors and other supporters that the inimicus Has Filed A Brief Before The Court expressing the timeless verities for which the inimicus and its supporters stand." Any departure from this purpose is frowned on.
In our briefs in Nike v. Kasky and United States Postal Service v. Flamingo Industries, however, I believe CAC made a valuable contribution. In both cases we brought up constitutional arguments that were not addressed at all by the parties. In Nike, we challenged the constitutionality of California's "private attorney general" statute under the Guarantee Clause of the Constitution (which requires all states to maintain republican governments rather than direct democracies). And in Postal Service, we argued the structure of the USPS violates the Supreme Court's requirements for a sovereign agency under Morrison v. Olson (which defines the difference between "superior" and "inferior" officers of the Executive Branch). Whatever impact our briefs had on the ultimate outcome (none in Nike; to be determined in Postal Service), we upheld our role as legitimate "friends of the court".