The best way to write a letter of recommendation is to start out with a formal greeting, or using "To whom it may concern" if you don’t know the recipient. Follow the greeting with 2-3 sentences of praise for the person you’re recommending.
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.