For the interview, make sure to bring anything asked for in your confirmation letter. The guy being interviewed next to me flunked since, as a self employed person, he needed to have brought evidence of financial worth (tax returns or something, I didn't pay that close attention).

The interview asks about arrests, convictions, things like that. Where you've traveled outside the US in the last 5 years. I thought it was more for the curiosity of the interviewer than any bureaucratic purpose.