Recommendation letters are written to help and support a candidate by presenting a better perspective of him/her. The aim of these letters is to present the candidates in a good light.
There are different types of recommendation letters, like Student recommendation letter, Employment recommendation letter, Fellowship recommendation letter and Character recommendation letter.
Recommendation letters are given importance depending on their source. So, it is important to write these letters on formal letter-heads as they would make better impact.
Typically, they must include facts about the period and kind of association you had with the person you are recommending. This helps in establishing your credentials as well as the extent to which you know the person.
It is a good idea to quote particular instances to highlight the positive points of the person you are recommending. This will give the letter an authentic as well as personal touch. Recommendation letters should bring out facets of the person which would not be known through an application or other sources of formal communication.
It is good to keep these letters short, simple and sincere. A page would suffice in most cases.