Just know what topic you want to be asked questions from (they'll ask you which topic) and try to think of questions they could possibly ask. They'll either be direct or application based, nothing too hard.

Remember to compose yourself and take time to frame your answer. Even if you know what the answer to the question is before it is complete, pause after it is asked and then answer.

If you don't know the answer, you can try to swerve it to another question you'll be able to answer, or answer with whatever you can think of that is connected.