Unless you have a criminal conviction or an arrest the process is usually relatively straightforward. Your sit in the waiting area will likely be longer than the interview itself.
Generally, at least in my experience, the interview has two parts. A review of the paperwork and the testing segment. The tests are clearly important and studying is key but the paperwork is also important. Not only does it need to be correct but you really should understand what is being asked on the questions towards the end of the application. For example, if you don’t understand what the oath of allegiance is and are asked about it, you may be sent away to come back another day.
So I recommend studying the last pages of the application as well as the test before the interview.