When deciding on whom to ask, don't simply think of those classes in which you have done well: think of instructors or supervisors who are most familiar with your work and achievements. Readers look for evidence of the letter writer's familiarity with your work. Without it, letters of recommendation lack credibility.

While you might be tempted to request a college letter of recommendation from a tenured academic superstar, refrain from doing so unless you know the recommendation will be strong. An impressive signature will not compensate for a lukewarm letter.