Target the recommendation. Is it for an academic post, a job, a volunteer position, a background check, or a personal reference? Write your letter so that it is focused on this purpose. For example, if the letter is part of a job application package, it should focus on the professional qualifications and conduct of the candidate.
Then, explain how you know the person and why you’re qualified to recommend them. Include specific examples of the person’s qualifications and successes in the body of your letter, then end with a sentence affirming that you recommend the person for the job or position.