Obtain concrete information about the qualification and experience of the candidate you are recommending, in case you know him but are not currently working with him. Ask the candidate to provide you with his updated resume and documents, such as research papers, that support his work experience. These materials are not necessary if you are working with the candidate and have firsthand knowledge of his work and skills.
Introduce yourself. Write about your relationship with the candidate. Explain the type of experience the candidate has had and the amount of time you have known him.
Provide the reason for your recommendation, giving specific details. For example, if you are recommending a candidate for a new academic position, you could explain how his research in his discipline contributes to the field.
Give a summary in the last section. Reiterate your support for the candidate and include key points that substantiate your recommendation in the summary.