How can I prepare for BITSAT 2017 on my own without any coaching classes ?

Study as per syllabus .Clear the concepts and learn the tricky methods of application of concepts .If you are interested for CSE,you may try IIITHyd.

If you don't want to enroll in any coaching centers, then you should be highly determined student , you need to be very disciplined. You have to refer to proper books for practice. NCERT books are a must Physics - HC Verma and Irodov Chemistry - Organic - Solemn and Fryle for concepts and Himanshu Pandey for practice questions Inorganic - JD Lee(best book) Physical - RC Mukherjee Maths- ML Khanna and G Tewani for calculus and for more practice and to attain a high level you can practice disha publications DPP. Also you are very much goal oriented which takes you a step ahead of other aspirants. You should try BITSAT sample test papers timely.