Here's a rough guide to how examiners decide what scores to give in the speaking test. At least, this is how I used to approach scoring when I was an examiner.
I'll look at part 1 of the speaking test today, and then I'll cover parts 2 and 3 over the weekend.
Speaking Part 1
Examiners are aware that part 1 questions are quite easy, and that candidates will only be able to give relatively short answers. Therefore, they are not expecting to hear any "super-impressive" language at this stage.
Instead, I believe that examiners are getting an overall impression of the candidate's ability in the following areas: pronunciation, avoiding mistakes in simple / easy sentences, answering without too much hesitation, speaking fluently without too much repetition.
Tip: Candidates perform better if they focus on answering fluently. Easy answers are fine; just make them as fluent and natural as possible.