I have found that the more I practise speaking in front of others, the less nervous I get in interviews. Perhaps try joining things like debate clubs (if your uni has one - or start your own). You could try recording yourself answering random questions on Zoom and watching them back. I have found that the more I practise implementing structure and controlling speed when speaking, the easier it is to do during an interview - even if I am a bit nervous.
Thinking about your answer whilst you speak is also not a good idea as you will be less in control of your answers and where you end up. I have found speeding up is a natural reaction when I don't feel confident in what I am are saying - I just want to get to the end of the answer as soon as possible so the awkwardness is over. A barrister once told me that his trick is an acronym called TUPA - Think, Understand, Pause, Answer. It's quite catchy and easy to remember