As the apllicants of the exam are usually the pass out class 12th batch of the respective year so the difficulty level of the exam isn't above the level of their class 11th and 12th syllabus, the topics that are covered in the exams are mainly the topics you can easily get in your 12th standard books so according to me you just need to go thoroughly through all of the topics from your school level or reference books but for a better preparation you may look for books like

• Arihant Wbjee Engineering Enterence Exam Solved Papers
• Understanding Physics Series - D.C Pandey
• Organic Chemistry ,Morrison Boyd
• Inorganic Chemistry, O.P. Tandon
• Numerical Chemistry, P.Bahadur
• Class XII Mathematics ,R.D. Sharma.
• Basic Concept Of Physics I+II, HC Verma.

Good Luck!!.