You may consider taking up classes from an institute like ACE as they provide good coaching for NTSE exams.

Ace your CBSE exams with ACE as it provides good coaching for CBSE.

Make a time table for yourself and dedicate time for all your subjects equally.If you are not sure about how to start and go about your studies, it is a good idea to consider taking up coaching classes. ACE offers good coaching to crack IIT-JEE. More details can be found on the website