Ask people who can speak to your qualifications for the program to which you’re applying. Faculty can speak to your academic abilities; advisors can speak to your professional direction and goals; internship or job supervisors (when appropriate) can speak to your experience and ability in the field. This is not the time for a “character reference.”
Ask in person. Make an appointment to meet with the person you plan to ask. Be assertive and say, “Do you feel like you know me well enough to write a strong letter of recommendation for (insert program/school/position)?” A tepid, unenthusiastic letter can be more harmful than you might want to think. If your potential letter writer indicates that she or he does not feel that they can write a strong letter, then thank them, move on and focus on finding another recommender.
Be sure to provide:
Ample time. Keep in mind that you are very likely to be one of many students asking this professor to write a letter. Allow at least 4-6 weeks for the letter to be written.
The name of the program and the degree you are seeking (the name of the school alone is not enough!)
A copy of your resume/CV
Pre-addressed and stamped envelopes for mailing
Contact information for the person/office who will be receiving the letter
Deadline by which the materials must be received
Expect to sign the waiver on the recommendation form that forfeits your right to see the letters written on your behalf. Not signing the waiver can make your reference uncomfortable and have an inhibiting effect. As much as you might want to see what your professor or supervisor has written about you, you’ll just have to trust that they’ve done what they said they’d do and that they’ve written a strong letter. If you really want to see it, you can always ask him or her directly. But sign the waiver.
After the letter has been sent
As the deadline approaches, contact the schools to which you have applied to check on the status of your application file. If any of your letters of recommendation are missing, contact your reference(s) and gently remind them of your deadline. Thank them again for their assistance. Your references have all applied to graduate school themselves at some point; they understand the critical nature of the deadlines you face. Send a hand-written thank-you note to each person who has written a letter on your behalf.
Send another one when you find out if you’ve gotten in. Good manners always count!