Write the letter to your Russian friend on letterhead. Letterhead makes your letter look more official and indicates you are a citizen with a business. If you cannot use letterhead, type your address in the top left-hand corner of the page.
Use the block format. In this style, you start all text flush on the left-hand side of the page. Leave a line between the parts of the letter --- return address, date, salutation (also known as the greeting), body of the letter and closing --- rather than indenting.
Enter the date, leave a line and write the salutation. "Dear Vladimir," and note that your friend's name is followed by a comma.
Get straight to the point: "I am writing to invite you to visit me in New York." Indicate that you are sponsoring your friend's application for a visitor's visa.
Specify the dates of your friend's trip. "I am looking forward to spending time with you from July 15th to August 5th, 2011." If your friend does not know what dates she will be there, write the text as follows: "I am looking forward to spending time with you as soon as you can get your visa to the United states approved."
Talk about some of the things you plan to do with your friend when she is in town. "As well as exploring Manhattan, we will also go to Chicago to see my parents, whom you met when they were in Moscow."
Indicate that the officials at the American Embassy should feel free to contact you if they want more information about your letter of invitation. Include your telephone number and email address.
Finish the letter with "Your friend," or "Yours truly," and then leave three or four spaces so that you have enough room to sign the letter. Type your name below the signature space.
Leave your letter for a while --- an hour or two should do --- before you edit it. Check your letter of invitation for typographical and grammar mistakes and correct accordingly.