Which books should I refer for CET Engineering

You need to go through well with HSC portion (class 11th and 12th) because the syllabus is based on that.

Here are some important tips you can follow:

You should be well aware about your HSC syllabus and topics covered in the textbooks. Most of the questions asked in this exam are based on the theories, definitions and concepts based on HSC syllabus. So prepare well and cover all the topics related to that subject.

Solve papers to understand your strong & weak points and strategise accordingly.
Try to formulate tricks for particular type of questions which you find time-consuming because MHT-CET is a test of your speed as well.

Divide your time well among all the subjects. All the subjects all equally important and need full attention to score high in the exam.

Try to solve as much MCQ as you can once you prepare the topic well. Many students do not score well in the CET exam despite of preparing well and this is because they are not familiar of the MCQ format of answering.

The books you can prefer:

Chemistry

Complete Reference Manual MH-CET 2016 Chemistry (Arihant Publication)
Chemistry for MHT CET (MCQ) by Mayur Mehta and Chitra Joshi (Marvel Publication)
XII: Sci. Triumph Chemistry by multiple authors (Target Publication)

Mathematics

Complete Reference Manual MH-CET 2016 Mathematics by Sushil Verma (Arihant Publication)
Mathematics for MHT CET (MCQ) by Hemant G. Ainapure (Marvel Publication)
XII: Sci. Triumph Mathematics by multiple authors (Target Publication)

Physics

Complete Reference Manual MH-CET 2016 Physics M.K. Dikshit (Arihant Publication)
Physics for MHT CET (MCQ) by A J Bapat (Marvel Publication)
XII: Sci. Triumph Physics by multiple authors (Target Publication)

Good Luck!