Send a letter of invitation to visit the United States to the party who is visiting so it can be taken to a U.S. Consulate office when that person applies for a visitor's visa, states All Law. Address it to the visiting party, but don't make it sound formal.
The letter should focus on the visiting party's specific plans while in the United States and give the dates of the trip, according to All Law. A few other things to mention are where the party is staying and how the cost of the trip is either already paid or that it does not require the visiting party to obtain a means of income while visiting. Also mention the purpose of the trip, such as events or specific places that will be visited. Consider including information about the party's transportation arrangements for the entire stay.
When you are providing financial support to the visiting party, fill out a United States Citizenship and Immigration Services Form I-134, or an Affidavit Of Support, in lieu of writing a letter, says All Law. This form is available on the USCIS website. Sending both a letter and a Form I-134 can increase the visiting party's chance of having a visa application approved.