Provide Your Recommenders With Specific Examples
The weakest type of letter is one that is too general—that lists your qualities but doesn't show them. The illustrative stories you provide (and you can do this in a bulleted list) should be unique for each recommender and should highlight the qualities you want the recommender to expand upon. These inputs will allow you to subtly influence the recommenders’ output and ensure the recommendation letters include concrete and varied examples that reinforce your existing application content.
Do Not Write Your Own Recommendation Letter
Your supervisor might say, "I'm too busy; you write it, and I'll sign it." If a potential recommender puts you in a tough spot and only agrees to submit a letter that you’ve written, it is best to move on. It is often obvious to schools when an applicant has crafted the copy because of similarities in voice to other application components.