For me, the interview questions were challenging when compared to other interviews that I've had. They were very thought-provoking and not your average "tell me about your best qualities and then one thing that you'd like to work on" type of questions. They had definitely put a lot of thought into the questions to make sure they were meaningful so they'd find the right candidate.
My advice is to be friendly, smile, listen carefully, make eye contact, and give a firm handshake at the beginning and end of the interview. It's also imperative that you ask questions about the job. My favorite is "can you tell me what an average day in the life of this job would entail?". That shows them that you are interested and really trying to make sure this job is the right fit for YOU, too.
Other than that, to prepare I would suggest you review the job description and requirements and think of a point for each. For example, if it requires you to have excel experience, then think of a time that you had a challenge with excel and how you overcame it. If the position requires you to work alone or with a team, think of answers and situations where you've done a great job with both, and what is your communication style.