Coaching institutes can only guide you. To get success or failure is totally depends on you. There are many students who have cracked their exam without coaching institute. 

You should go with NCERT books for your preparation alongwith previous year questions papers. Here are some other preparation tips you can follow.

Make you own time table , Shorter and achievable small targets.

Focus on limited books - NCERT + Some reference

Finish your full syllabus in a fixed time frame of 3-4

Solve MCQS daily in a time limit - Understand where you are doing most mistakes, Correct it, retry

Whatever you study throughout the day make sure that you revise before going to the bed

Concentrate More on weaker subject

Give equal important to all the three subjects.

Understand all options of previous year MCQS

Give mock test in between to assess yourself.

Good Luck!