CLAT Preparation

There is nothing like best books for CLAT. There are good books which help in preparation. First I would recommend you the books which are widely used for this exam and then I will give my strategy/preparation tips. A) English - Word Power Made Easy (Vocabulary), Any RC booklet, Grammar rules can be done through videos available online/coaching classes (there are books like Wren and Martin also), idioms and phrases can be done from the numerous sources available on the internet. B) Mathematics - Quicker Maths by M. Tyra, Quantitative aptitude by RS Aggarwal
c) Legal Aptitude - Universals guide to CLAT and LL.B. Pearson CLAT Guide by Gargani et cetera
d) Logical Reasoning - MK Pandey for verbal reasoning, RS Aggarwal
e) GK - For static, people refer Arihants guide.

From your question, it sounds like you're interested in classroom coaching centers. If that's the case, I'd suggest doing your homework thoroughly - there are quite a few institutes that charge hefty fees without providing anything in the name of quality. Here are some basic tips to keep in mind:
Quality of the faculty - many places hire recent Law grads who couldn't land a job or pretty much anyone else who can teach. Check that you are being taught by someone who actually knows what they're talking about and are qualified to teach
Results of the institute - however this is hard to verify because all coaching classes claim the same few students as their own, when in reality the student may have once visited the branch for a mock test or something
Your commute - if you're going to be visiting the same place for several months, it better be convenient for you otherwise you're going to be wasting a lot of time commuting.