These are core suggestions which you are free to embellish/expand on. However it needn't be long. Three short and to the point paragraphs.
Should describe your relationship to the applicant. How you met. Have you stayed connected? Why you remain friends.
Second Paragraph/About Brad:
In this part of the reference letter, give your impression of the persons good character. An assessment of their good behavior and law-abiding nature. It’s essential that you give an example of their character, if possible . Are there any examples that come to mind while working together, travel, sports, etc. You could use words like:
At the end of the letter, you could include some kind of complimentary statement in conclusion.
* “I would not hesitate to recommend Ms. ___________.”
* “I have complete trust in Mr. ___________.”
* “I believe that Mr. ____ is a good candidate for a U.S. Visa Waiver renewal.