Create a list of possible individuals from whom you can request a letter of reference. If you are asked to provide two letters of reference, have a list of four or five individuals that you can request to do a reference letter for you. You may already have made a mental list of people to ask. It's important to think about the relationship you have with the each person, since the letters that they write will be sealed. Never open a sealed letter of reference if you are delivering your entire application package together in person or by mail.
Check with the school or department that you are applying to in order to determine if there is a form that must accompany the letter. Often the reference provider will also be asked to complete a short questionnaire rating the student in several key areas. If there is not a form, there still may be guidelines that the reference writer is required to follow.
Contact the individuals that are at the top of your list. If the person hasn't heard from you in a while, an in person visit may be more appropriate. You may need to refresh this person's memory. If you are asking a former instructor, it's important to remember that you are one of many students that he has taught over the years.
Write a respectful letter or email if you are not visiting in person, offering information about your goals and any achievements that will help support your request. For example, if you have recently completed a summer job working for a veterinarian, point out this fact in your request and how it inspired you to apply to college with a goal of becoming a veterinarian. Also include any influence that the instructor had on your goals and how, in part, that influence caused you to pursue your current course.