Hello

Solving previous year papers and mock tests help a lot in preparation of the exam. It helps in enhancing the speed.
You should try to understand the complete syllabus and refer the NCERT textbooks and other advanced books for in depth knowledge.

For preparation of the VITEEE exam, You can enroll for the VITEEE Knockout to prepare for the exam more effectively and smartly using the smart study material (which includes chapter wise, concepts wise, most asked and most difficult questions), Advanced Test Series based on VITEEE Pattern (which includes unlimited chapter wise test, subject wise test and full mock test), adaptive time table, performance analysis (which includes Prepmeter, Strength Sheet, Weakness Sheet, Skills Graph) and Rank Predictor tool.
Go through the link below to check the details-

http://bit.ly/2Uyp81K

Good Luck!

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Read NCERT textbooks of 11th and 12th standards of Physics, Mathematics and Chemistry. 

Practice questions from NCERT textbooks. Know the concepts and understand them. If concepts are clear then a student can solve an easy and difficult both types of questions. 

Practicing past years papers would help you but don't forget to read textbooks. 

If you still have any queries feel free to ask in the comment section down below.