IELTS is a really challenging test that is jointly managed by the British Council, IDP: IELTS Australia and Cambridge English Language Assessment and requires serious preparation of the candidate. Whichever way of preparing for the test you choose, the only thing that remains unchanged is your vocabulary. It's clear for all that in order to get a high band the candidate must have a large English vocabulary that can cover a lot of narrowly specialized subjects that are rarely found in everyday communication. Therefore, even for people who speak English well it's needed an additional preparation for IELTS test.