Here are three tips, one for each part of the speaking test.
Part 1: stop and smile
For part 1 of the speaking test, you need to get used to giving short answers. Many students find it difficult to stop speaking, and the examiner is forced to interrupt. My tip is to give your answer then stop and smile, showing the examiner that you are ready for the next question.
Part 2: tell a story
In the context of speaking part 2, a story is simply a long example to illustrate a point that you have made. If you’re describing a person, for example, you could tell a story to illustrate why you like him/her. People find it easy to keep speaking for longer when they have a story to tell.
Part 3: include an ‘if...’ sentence
Look at technique number 2 in this lesson. The 'alternatives' technique helps you to say more, and it also encourages you to add a conditional 'if...' sentence, which might help your grammar score.