I'm afraid I will have to disagree with a portion of the above suggestions. While plagiarism in some sense is acceptable (in terms of formatting), you'd do best to try to stand out amongst the crowd rather than blend in. That's the whole point after all. Much like evals/fitreps though, the CONTENT is what will be looked at much more than the format. For years the debate about which key phrases will do the trick etc. But in reality, it's the actual achievements stated in the write up that will carry the day more than anything else.
With that said, I would simply suggest using "active voice" rather than "passive voice". Meaning, write each sentence in a Subject, Verb Object style rather than the other way around. It states the same information, but it does it in a stronger way.
Also, try to stay away from overused adjectives and verbs.
And lastly, end a recommendation letter with a VERY STRONG, unambiguous statement that gives clear direction (in the form of an "action step") for the board. "John Doe is already performing in the manner of (whatever you are applying for). Select him immediately!" Something bold like that will help you stand out from the many: "This is a good guy that I am recommending because I want to be a good guy too." type conclusions.
Hope that helps. And good luck!