MOST IMPORTANT: Remember to listen to the questions asked by the interviewer/immigration officer and answer only the question asked.
It is important to review important dates, your spouse's date of birth, ages of siblings. Have you met your spouse's parents? If so where and under which circumstance?
Immigration officers also may ask about the location and color of certain items in the marital house. It is also good to know who your neighbors are and if they have any children. Review gifts you exchanged for anniversaries and other special events. Body language is essential. Make eye contact with the officer and always be honest.
It is also important to get a good night's sleep the night before the interview. Going through a mock interview with an attorney is an excellent way to prepare.