What you need to know:

Present a primary ID to the Acceptance Agent. The ID must have been issued at least six months prior to the application date.
If your ID and legal name do not match, provide a copy of the legal document showing the name change.
If your ID was issued less than six months ago, submit as many additional forms of identification as possible. The U.S. Department of State may still request further proof of identity.
If you do not have a long-form birth certificate, you can order one here.

Primary Forms of Identification

If you don’t have the primary identification documents listed above, you can provide alternative identification documents.
There’s no guarantee that the U.S. Department of State will accept these documents, so it’s best to provide as many as possible.
Documents that include your photograph, signature, and/or physical description are particularly useful.