First of all, you should assess your English knowledge in four skills (reading, speaking, listening and writing). Studying Cambridge IELTS (volumes 4-9) is the sources for an IELTS taker. Reading articles (in newspapers and magazines (especially Economist, Times,...)) is a mandatory component for preparing IELTS. Furthermore, you should practice to fortify your skills in scanning and skimming texts.

I had a friend take an IELTS English exam and do well. I just had her take lots of practice tests (like the ones found on http://www.examenglish.com/IELTS/cbIELTS_reading.htm) and checked them for her, explaining any mistakes found.