Discuss your need for references with the potential writer. Ask if he or she feels comfortable supporting your candidacy and has time to write a letter in the next two to three weeks. Recognize that your reference writer is undoubtedly busy and that writing a good letter will take some time, so don't demand it immediately. If you detect reluctance, allow the individual to decline gracefully. Letters produced unwillingly won't be of much value.
Most individuals have preferences.
Provide background information. After you've lined up an advocate, make an appointment to discuss your letter and provide background information about yourself. For every comment the writer makes about you in the letter, there should be supporting evidence. Thus, the more specific information you leave with the writer, the better he or she can comment on the qualifications you have. Clarify the letter's purpose.