The only way is practice. Physics specially requires a clear understanding of concept and practice. Without the former, the latter would fall. So, try understanding first clearly and to do that you may use NCERT, Reference book or a guide. I would prefer guide because it would decrease your time investment in reading theory.

Next get hands in some good objective books like NCERT at your fingertips, DC Pandey Medical etc.Once you complete a chapter in these level books go for engineering level if you aspire for AIIMS and JIPMER. 

Chemistry the theory level is a bit more high so read NCERT thoroughly for inorganic. Organic and physical needs practice and the same strategy applies.