Use a formal salutation
State your relationship to the person
Mention how long you have known them
Explain the context in which you worked with them
Highlight their key strengths
Give specific examples of their achievements
Describe relevant skills and qualities
Compare them favorably to peers if appropriate
Mention why they are a strong fit for the opportunity
Include a clear recommendation
Offer to provide more information if needed
End with a professional closing
Include your name, title, and contact information