Prospective employers, graduate schools, and scholarship foundations may ask for one to three letters of recommendation that support your application.
Depending on the application, your recommenders might be professors or staff at your school, employers at jobs or internships, or supervisors of community leadership and volunteer activities. Your recommenders will be asked to comment on how long they have known you and in what capacity; their recommendations will be taken more seriously if they can show they know you well.
Help your recommenders as much as possible, by providing accurate instructions and background information. (See what will your recommender need from you?)
It's important to establish relationships with teachers, supervisors and mentors who are qualified to comment on your academic accomplishments, work habits, personality, and likelihood of success. Even if you're not planning to apply for anything just yet, keep an eye out for suitable recommenders.
You may want to ask a supervisor at the end of a successful internship, or a professor in whose class you did well, if they would be willing to write a letter on your behalf. A recommender might agree to be contacted in the future, or might choose to write a general letter of recommendation right away, for you to keep on file. (See how to store and send letters of recommendation).
Give your recommenders plenty of advance notice. It's not only good manners, but also allows time for composition of a thoughtful letter that can effectively support your application. Asking early also gives you a chance to find another recommender if your first choice is busy, absent, or reluctant.
If you're on campus, make the request in person. That way the professor gets a chance to ask about your goals and plans, and you get a chance to gauge the professor's willingness to write a positive letter. If you've graduated and left the area, you'll need to make the request by phone or in writing. It might be a good idea, especially if it's been a few years since the professor has seen you, to attach a small photo of yourself to your written request.
Ask your recommender if he or she would be willing to write a good (i.e. strong, supportive) letter on your behalf. Don't assume - some people will agree to write letters only for students they know very well, or for students who did well in their classes. Some will not agree to write letters unless they have several weeks' notice, especially at busy times of the year. (Should you decide not to follow through with your application, be sure to let your recommender know immediately.)
Always check in with your recommender several days before the letter is due. Sometimes even the most organized and conscientious recommendation writer will appreciate a reminder. A thank you note is always in order when someone writes a letter on your behalf. Be sure to let the recommender know about the outcome of your application.