One of the best things you can do to prepare for an interview is to research the interview questions Big 4 firms most commonly use, and practice them ahead of time. Getting together a list and practicing the Interview questions is essential because it makes you more calm, look professional, and come off as a better candidate.
Write down your answers and practice answering them. Make sure you actually say your answers out loud as well. Many times we think something sounds good, only to speak it out loud and completely lose confidence. Have a friend to help you practice by reading the interview questions and having you answer them. Doing this makes you less nervous for the real thing as well as get your your response more fluid.
There is a limit to how much you should practice your interview Q&A, however. It is important not to just read off what you memorized because it will show and you will sound like a robot. Instead, have the answer as a base for discussion and have an actual conversation, not a speech.