Make comparisons to illustrate their success. To put the candidate’s accomplishments into perspective, include comparisons so that the recipient will have some basis to understand why you are recommending this person.
Inform yourself about the person you are recommending. Spend some time talking to them about their goals and the position they are applying for. Gather together their current resume, any memos or notes you may have on them, and any other information that will help you as you write the letter. The best recommendations are thorough and specific, and having all the information at hand will make the process much easier.