In most cases, agree to write a letter of recommendation only if you can honestly write a supportive letter. If you cannot portray an individual positively, decline to write the recommendation.
Ask for a current résumé and as complete a description as possible of the position or program to which the person is applying.
Assemble and review all other relevant information you may have about the person you are recommending. It is often easy to overlook some important accomplishment.
Writing the letter:
Present the person truthfully but positively. A recommendation that paints an unrealistic picture of a candidate may be discounted. A recommendation that focuses on negative qualities may do more harm than intended.
Tailor the recommendation to the position. A letter recommending an individual for a job as a camp counsellor should contain different information from that in a letter recommending the same individual for a job as a computer programmer.
Begin the letter by describing how you know the individual you are recommending and the specific contexts upon which you are basing your evaluation. In what situations have you known the individual? For how long? How closely?
Present the individual's general qualities relevant to the position along with one or two detailed examples. Including vivid detail will make the recommendation much more effective.
In most cases, a letter of recommendation should consist of three or four paragraphs and not be over one page in length.