Step 2: In the first paragraph of the affidavit, put the name and personal background information of the person giving the information. This article provides a comprehensive sample of an affidavit letter, guiding readers through the essential components and format.1. Talk to the person immigrating to the US. The person for whom you write an affidavit should be someone you know very well. One form of substitute document that you might need to use is what's called a "sworn declaration. CitizenPath has prepared a downloadable I751 affidavit sample that you can forward to friends who are willing to write a letter of support.