A good reference letter will establish credibility by having a figure of authority focus on and verify your accomplishments, contributions, motivation, attitude, and reliability. To do this, the person you chose to request a letter from must have some degree of objectivity, as someone with a close personal relationship could be judged to be biased. Thus, if you are asked to write a letter of reference it is important to state how you know the candidate, and in what professional capacity, before you begin discussing any positive personal qualities (with specific examples). Your recommendation will then hold more value.