Hi Janbhadur, 

Yes,  it is a good decision to drop an year and prepare for CLAT exam and especially for the top 5 National Law Universities. Coaching will give you the right kind of guidance and material to study from but please do not depend on the faculty for everything and make sure you give as many mocks as possible. Do far as class 12th % is concerned it is not counted and is only considered for checking eligibility which is 50% I think.