i practice a lot numericals but fail to perform well in numericals that appear in exams

Since, you are saying that your theory is pretty strong but you fail to apply that to the application based questions and numericals, I would recommend that you practice as many questions as possible. Pick up NCERT and Pradeeps (HC Verma too if you want to doa  little difficult problems) and solve all its question using a pen and paper. That will probably give you a better idea of how to apply theory to numericals.