There are lots and lots of different IELTS Speaking Part 2 Topic cards (see example below) and you can't prepare for all of them, but you need to plan, prepare and practice for as many as you can.
It is only through repeated planning, preparing and practising that you will become proficient in this section of the Speaking test.
Here are some basic tips:
Become very familiar with the format of Speaking Part 2 Topic cards
Use the bullet points on the card to structure your answer
Plan what you will say using this structure to speak for 90 -120 seconds
Practice by using notes - NOT reading sentences
Record and time yourself.
Practice again. Reduce any repetition and long pauses.
Speaking structure tips
(1) You DON'T NEED an introduction, for example:
'In the world today, there are many different ways of communication, among them my favourite way of communicating is ....
None of that, just start directly and use synonyms if you can. For example:
My favourite method of keeping in touch with people is by using mobile phone and the internet.
(2) You DO NEED a conclusion, for example:
'So, that is why using a mobile and the internet are my favourite methods of connecting with people'
Plan, prepare and practice (PPP) and you will become more proficient.