Most of my replies were completely unplanned, I think that the interviewers appreciated my spontaneity somewhat. Because I'm naturally quite modest, I just practised talking about myself with family members, and also answering some random potential questions that they'd ask me unexpectedly at various points over the weeks coming up to my interviews. I had three interviews and received two offers (I got rejected from Newcastle which was my first interview, so nerves got the better of me).
Edit: Also with regard to how I answered the questions, I tried to talk around the topic, but without straying into their next question. (I also found it useful to pause for a moment before beginning to answer, allowing me to collect my thoughts)