For example, your family doctor should not write a letter of recommendation for your employment or college entrance application if neither have anything to do with the medical field and you have not worked in his or her office.
Make sure the person you request to write your letter has the time and, more importantly, the inclination to write an effective letter of recommendation.
Remember, a good letter of recommendation is one part of a multi-level strategy.
If you really can't provide a letter of recommendation for someone because the negative outweighs the positive, find a tactful way to say no, express regret and offer a suggestion as to who else might be a better alternative.
Friends, employees, co-workers, and business associates may ask you to provide a letter of recommendation to potential employers.