In my posts and materials, I present lots of useful expressions for asking the examiner to repeat something, gaining time to think about what to say next, expressing an opinion, connecting your ideas, etc.
However, you should use always these expressions in a natural way. Do not use them only to impress the examiner! Let me give you a couple of examples.
Time fillers
In my materials, I teach some useful expressions you can use if you need to gain time to think, for example:
Hmm…that’s an interesting question.
It is natural to say this if the examiner asks you a question that really is interesting in some way, for example:
Examiner: Do you think people are healthier now than in the past?
Candidate:Hmm…that’s an interesting question. I think in some ways we are healthier, but in other ways we are less healthy. …
However, if you use the expression after a simple question, you will sound unnatural. Examples of simple questions include:
What is there to do in your town?
Do you work or study?
How did you travel here?
These are generally not ‘interesting’ questions, so if you need time to think, use a different time filler.
Expressing an opinion
In my eBooks, I teach lots of useful phrases for expressing an opinion. Here’s an example:
I’m absolutely convinced that …
It is natural to use this expression if you have a very strong opinion, for example:
I’m absolutely convinced that smoking should be banned.
Although this is a very nice way to express a strong opinion, it is unnatural to use it if you do not feel so strongly about something. For example:
Examiner: Do you think that English is a difficult language to learn?
Here, it would be more natural to begin your answer with something like:
Personally, I find English quite difficult, because my language is totally different. …

You can find many more tips like this in the IELTS Speaking Masterclass course, an essential programme of training materials for IELTS Speaking including videos and downloadble pdfs.
Thanks for the useful tips,I learned something new.
cheers
Helen
I like to take part In your online ebook study…I tend to get a good band score in IElts test..so,I think you would provide me a number of usefuls tips…
great it is useful for me.