You need to ensure these things -

1. You know the concept in deep. You can check this by solving level-1 questions ie. conceptual questions.
2. You are able to solve conceptual, fact based and formula based questions this is to check whether you remember the things or not.
3. Then check whether you are able to solve level -2 (JEE Mains level) and level-3 (JEE Advanced) questions, if not then try solving examples of the level in which you are stuck.
4. Now see the concepts on which questions are being asked in previous year JEE Mains and JEE Advanced.

Now you are ready for the exam !