Basic requirements include: a passport, passport photographs, birth and police certificates, marriage, divorce, or death certificates, proof of financial support, and medical examination.

The priority date, in the case of a relative immigrant visa petition, is the date the petition was filed. In the case of an employer-sponsored petition, the priority date is the date the labor certification was filed with the Department of Labor. The State Department Visa Bulletin is a monthly publication that gives the changes in availability of priority dates.

Access the Visa Bulletin online, by email, by telephone, by fax, or by mail.

Online: http://travel.state.gov/visa_bulletin.html
Email: VISABULLET@SA1WPOA.US-STATE.GOV (you may contact the Bulletin by email, but it is not distributed by email)
Telephone: (202) 663-1541, for a 24-hour recording that gives the monthly priority dates that are currently being processed. The recording is updated in the middle of each month with information on cut-off dates for the following month.
Fax: From your fax, dial (202) 647-3000. Follow the prompts and enter code 1038 to have the Visa Bulletin faxed to you.
Mail: To be placed on the Visa Bulletin mailing list (or to change an address), write to:
Only addresses within the U.S. postal system may be placed on the mailing list. When reporting changes or corrections of address, include a recent mailing label. The Postal Service does NOT automatically notify the Visa Office of address changes. (Obtaining the Visa Bulletin by mail is a much slower option than any of the alternatives mentioned above.)

Make a copy of your Naturalization Certificate. Send the copy - NOT the original - to the National Visa Center, 32 Rochester Avenue, Portsmouth NH 03801-2909, with a letter containing the beneficiary name and case number of the petition you want to upgrade. The National Visa Center will send the beneficiary any additional forms and information that may be required.

Write to The National Visa Center, 32 Rochester Avenue, Portsmouth NH 03801-2909, or fax your new address to 603-334-0759. Be sure to include your case number or your USCIS receipt number.

Each country has its own requirements for obtaining police certificates or clearances. Specific information is available from the U.S. Consulate your case.