Many students only do one thing to prepare for writing task 2: they write lots of full essays. Although it's obviously important to practise writing full essays, there are other things that I think you should be doing.
Here are some study ideas for writing task 2:
1) Break the task into parts
Instead of writing a full essay today, why not try writing 5 different introductions using my 2-sentence technique? Or challenge yourself to write 3 different main-body paragraphs about "advantages" (e.g. advantages of mobile phones, homeschooling and immigration) - use this lesson to help you. Or write 5 different conclusions - just one sentence each, summarising your response to 5 different questions.
2) Do some research
Instead of worrying about one particular question, try to find 10 recent exam questions (maybe using this page). Write the questions on a piece of paper, decide what the general topic is for each one (e.g. advertising, prisons, life expectancy) and do some research about those topics. Don't worry about the exact question, just try to "collect" good ideas and vocabulary for the overall topic. A quick search on Google or Wikipedia should give you what you need.
3) What do you believe?
A big problem for some students is that they don't have well-formed opinions. They're not sure what to write about topics like homeschooling, immigration or gun control. The good news is that there is no 'correct' opinion - the examiner is only looking at how well you express your opinions in English. So, after doing some research (see point 2 above), make sure you have an opinion of your own.