Point out different details of the applicant's job experience. There probably are a few other people writing letters, so mention different abilities and skills to make your letter stand out.
Ask the applicant to give you an outline of professional duties and projects he has handled at work so you have a clear idea of what he has done.
Emphasize achievements and awards. Due to competition, the letter should highlight successes in the applicant's education and career experience.
Mention flaws that are accurate instead of giving broad statements like, "He works too hard." Instead, focus on skills the applicant can improve on, such as allocating time or being more prepared.
Include your signature at the end of the letter. Schools realize some applicants write their own recommendation letters, so signing the letter shows you wrote and reviewed it.