Do not be afraid to ask questions if they arise during the interview, even if you did not have them listed before the interview.
After the interview, you will need to transcribe (copy) exactly what was said during the interview. This can be a very SLOW, and timing consuming process, but it is critical that you copy exactly what was said.
After you have copied out the interview, replay the interview again and compare it to your notes. Make any CORRECTIONS necessary.
Share the written copy of the interview with the participant to make sure that they agree with, and affirm the contents of the interview.