But what to study ? How to prepare myself for CLAT 2018 ? which I must refer and study ???

Hello Richard Roso Yagou, if you are going to prepare for clat then you must have to focus on reasoning and vocabulary because this are going to help you in legal knowledge as well and other aspect is general knowledge which is very rapid section which can score you maximum marks in lesser time. for reasoning and maths you can follow R.S. aggarwal and analytical M.K.pandey and english arihant and word power are best follow current affairs for g.k. there are many open mock tests on inernet you can give and many other coaching centres are providing study material online also. study hard good luck

Firstly know the syllabus of CLAT 2018. You need to focus more on the topics to study-

Quantitative Ability
Number System
Average
Percentage
Profit and Loss
Time Speed and Distance
Cube
Time and Work

Logical Reasoning

Non-Verbal Reasoning-
Number and Letter Series
Odd man out
Coding and Decoding
Calendars
Symbols and Notions
Liner, Circular & Grid Arrangement
Distribution
Verbal Reasoning
Direction Sense and Blood Relations
Statement and Assumption
Statement and Conclusion
Strong and Weak Arguments
Course of Action

English
Grammar
Correct use of sentences
Spotting errors
Sentence correction
Idioms & Phrases
Foreign Words

Legal Aptitude
Torts
Contract
Criminal Law
Constitutional Law
Legal Terms

G.K & Current Affairs:

Current events
Legal judgements
Sports news
Business news
Political news
Film & television

The books you can refer given below-

Analytical Reasoning by M. K.Pandey
Objective Arithmetic by R.S. Aggarwal
Verbal Reasoning by R.S. Aggarwal
Analytical and Logical Reasoning by R.S. Aggarwal

You can also refer Career Launcher Material.

Good Luck!