When requesting a letter of recommendation from your supervisor, it's essential to provide them with all the necessary information to ensure that the letter is accurate and complete. You should provide them with a description of the position or program you are applying for, the specific requirements or guidelines for the letter, the application deadline, and any relevant materials such as your resume or CV. Additionally, provide your supervisor with a list of your accomplishments or key projects you worked on together to help them draft a more specific and detailed letter.