How can i prepare for ielts exam?

You can buy some IELTS books for self-studying. This link may be helpful to you. http://tutorials4share.blogspot.com/2011/08/good-books-preparing-for-ielts.html

Speaking with native speakers is a really good way to prepare as it will improve your speaking and listening skills. You can also chat to random English speakers on social networking sites to improve your reading and writing :D It may also be a good idea to write stuff like a diary in English. Hope this helps x

You need not join a class but you definitely have to prepare. You will then learn the format and tips to do well on the exam. First take a diagnostic test (Available online) and see your score and decide whether self preparation is enough or you need a course.. If you get a score below 6 in any section, then I advice you to join in any course. If you get more than 6, then just download or buy material and sample papers and prepare for around 2-3 months and write the exam.

There are many IELTS self-studying books. You can buy some of these and study all by yourself. But I advise you prepare somehow. I studied English for a long time as well and I am up to sit IELTS too, but I wouldn't dare not to prepare. It also depends if you are doing Academic module or General. If you are up to Academic module you should prepare yourself. I guess, preparation for General module is not really needed. As for the books, I would recommend IELTS 7 from Cambridge ESOL. It has 4 samples of the whole test. It is really useful to try that. Then there is a brochure called Common mistakes at IELTS Advanced which is quite useful as well. So yes, you should prepare for the exam.