3.1 Formal Invitations. Use the formats below for formal invitations and follow these rules of thumb.The following examples provide general guidelines. You may write a letter in English inviting your guest to visit you. Include in the letter (1) whom you are inviting, (2) the purpose of the visit. Invitation Letter to Apply for Visa. US Visa Information. Miami-Dade County Public Schools. To find out what's happening in your area. Regional Offices > Southern Region.