Sleep is something we all do unless you are an insomniac. If you are one, make sure you tell the IELTS examiner if you get this topic, as it will impress him/her.
Some of the questions you could be asked in Part 1 about sleep:
• How many hours do you sleep each day? • Is it necessary to take a nap every day? • Do old people sleep a lot? Why? • What time do you usually go to bed? • Do you always have a good sleep?
It is useful to know collocations/idioms about sleep such as:
an insomniac - a person who is regularly unable to sleep to suffer from insomnia - to not be able to sleep to take a nap - to have a short sleep to nod off - to fall asleep (for example, when watching TV) to hit the sack - to go to bed to be a light sleeper - to wake up quickly (for example, if someone makes a noise) to be a deep/heavy sleeper - to not wake up quickly or easily