For IELTS, what I did was:
1. I alloted 1 week for each component of the IELTS exam (1 week for reading, 1 for writing, 1 for speaking and 1 for listening)
I used different materials, but the most similar the the IELTS exam is the official IELTS review materials.
I also watched the Australia Network's "Study English" DVDs. You don't even have to buy them, If you register in British Council, they have the DVDs which you can watch for free while you are there. They also have the official review materials I was talking about (and a plethora of other materials: books, practice tests, DVDs).
They are open from 9AM to 4PM. Their staff are also very friendly, they will assist you with whatever questions you may have. PLUS it's so hot these days, you might as well take advantage of their A/C.
Personally, I don't recommend review centers. I think they are a waste of money. I prepared for the IELTS myself and I got great results. But then again, I was confident with my English skills, because we speak English at home and I was a writer back in high school.
If you are not so confident with your English skills, I recommend getting a private teacher (even a friend who is good in English) instead. Someone who will be able to check your written work and give you corrections. I don't think they give that much focus to students in review centers because students are admitted in bulk.