Your Fiance will need to prepare for the interview at the U.S Embassy, and will need to bring the required documents.
Completed Form DS-160, Online Nonimmigrant Visa Application.
A passport valid for travel to the United States and with a validity date at least six months beyond your intended period of stay in the U.S.
Divorce or death certificate(s) of any previous spouse(s) for both you and the U.S. citizen sponsor
Police certificates from your present country of residence and all countries where you have lived for six months or more since age 16 (Police certificates are also required for accompanying children age 16 or older)
Medical examination
Evidence of financial support (Form I-134, Affidavit of Support)
Two (2) 2x2 photographs.
Evidence of relationship with your U.S. citizen fiancé(e)
Payment of fees (MRV Slip, proof of payment receipt)