Dr. IELTS: A natural answer is the best answer. Talk to the examiner like they are people and have a natural conversation with the person sitting across from you. In general, the more you talk, the higher your score could be. Conversely, if you don’t say very much, you WILL get a lower score. Do not speak like a robot as that will indicate memorization. If you have a natural conversation with the examiner and can be natural across all three parts of the test, you will more often than not get a 6 for speaking. Some examiners will want to hear certain answers, which is not good, but their purpose is to have a constructive conversation with you. It is ok to stop and pause to formulate your answer as English is your second language and the examiner must allow that. However, keep in mind this is a timed test, so make the answers count.
Another thing examiners are looking for is a direct answer to the question. It sounds obvious, but many candidates try to "talk around the question" by going off from a keyword they listen to. For example, a part 1 question like, "Have you lived in your area for a long time?" Many candidates will start introducing their hometown because they might not know what "area" means. If they had listened to the introduction of part 1, "Let’s talk about the area where you live at the moment," then the candidate should know the question is about the place they live in now, not their hometown (unless they still live in their hometown of course).
Another example is, "What do you like about your studies?" A lot of candidates will start off by saying what they don’t like about their studies. THAT WASN’T THE QUESTION. Answer with what you do like FIRST. If you really don’t like your studies, talk about a teacher you like or a part of the school you like as these are still relevant to every student’s studies. If candidates don’t directly answer the question throughout the test, then the best they will get for vocabulary is a 5.
Dr. IELTS: If whatever you say is off-topic to the part 2 topic, then, of course, it won’t be good for you. Stick to the four points and the topic given. The purpose of part 2 is to see if candidates can produce enough language for a certain amount of time, in this case, two minutes. If you can’t speak for the whole two minutes, that is a good indication the candidate is unable to produce enough language and it will weigh the score down, making part 3 that much more daunting.
Dr. IELTS: It shouldn’t affect the score too much if the candidate can say it error-free the second time. Try not to make too many mistakes and more importantly, don’t make the same mistake twice. Remember, we know English is your second language, so we know you will make mistakes. If you can keep them to a minimum, then your score will be higher. For grammar, even a candidate that scores an 8 will make some basic errors (taken from the scoring rubric).