In part 1 of the speaking test you need to give short, direct answers. When you've given your answer, you should stop and wait for the next question.
The problem is that many candidates keep speaking, even when they've already given a good answer. Sometimes it's because they feel nervous about leaving a moment of silence. As they keep speaking, they start hesitating and repeating themselves, making the answer sound worse and worse. A further problem is that the examiner has to interrupt the candidate in order to move on to the next question.
The solution that I practise with my students is this: stop and smile! When you've answered the question, stop confidently and smile at the examiner to show that you're ready for the next question. If you can do this, part 1 of the speaking test will go more smoothly.