Open with a short, but enthusiastic, bit of praise. Let the company know right off the bat that you believe in this person. You don’t have to be over the top or insincere, but a positive note to start will make a big difference. It makes me extremely happy to recommend Michael for the position of Director of Development at XYX Corporation. Any company should count themselves lucky to have an employee as bright, friendly, and dedicated as Gina. No matter what she does, Helena Bonham does it well.
Break down the letter into short, but specific, paragraphs. Don’t ramble, but do flesh out your key points. Try to keep it at one page, covering the various aspects of their recommendation in brief, specific detail.