What strategy to be followed to get above 50 - 60 marks out of 100 in WBJEE 2018 from only Mathematics? What books are to be followed?

For mathematics section you need to practice a lot. Also, learn to solve probability problems using the tree method. Learn to solve problems and visualize them using graphs. It is recommended to solve miscellaneous problems from the S.N. De books of classes XI and XII.

Below are the important topics with weightage you should focus more.

Vectors (7%)

Probability (7%)

Three-Dimensional Geometry (6%)

Matrices Determinants (5%)

Limits (5%)

Indefinite Integration (5%)

Sets, Relations & Functions (5%)

Definite Integration (5%)

Theory of Equations (4%)

Permutation & Combination (4%)

Complex Numbers (4%)

Good Luck!!

I would suggest you to go through the below preparation points as these will be helping you -
1. Know your Syllabus Well.
2. Work on a Time Table.
3. Make your Basic Concepts Strong.
4. Improve your Weak Points.
5. Write Notes and Prepare Flash Cards.
6. Attempt Mock Test and Solve Sample Papers.
7. Revision is reallu must.
8. Make Sure to take breaks.
9. Check out Proper Books for Preparation as there are many available in the market but netter to focus on standard books which make all your concepts clear and strong and which are easy to understand.

Books which you can follow -

Physics -

The concept of Physics Part 1. HC Verma

The concept of Physics Part 2. HC Verma

Understanding Physics Series D. C Pandey

Chemistry -

Organic Chemistry Morrison Boyd.

Organic Chemistry O.P. Tandon

Inorganic Chemistry O.P. Tandon

A modern approach to chemical calculations R.C. Mukherjee

Numerical Chemistry P.Bahadur

Concise Inorganic Chemistry J.D. Lee.

Maths-

Class XII Mathematics

Trigonometry, Geometry Books

Problems in Calculus

Higher Algebra

Hope this helps!!!