to get in best nit cse u had to score minimum of 230 in jee main 
and two subjects will not able to get it so i advice u to spend maximum time on maths
first start with 11 , there is arihant series of maths by amit aggarwal and sk goyal ,  these books contain bot solved and unsolved which would be of great help for u .
for eg complex number is chpater with theory and tricks both so do it efficiently.
hope that u understand my point focus firstly on ur weakest and importaant chapters
 
approve if useful
						

							
prepare well for exam
concentrate more on your weak subject
but should not neglect other subjects revise them
all the best
						

							
Stay focused on your studies and keep in mind that one must focus on Physics, Chem and Maths, try to fortify these three, take some coaching classes from a reputed place like Akash Inst etc, then to download previous years’ question paper of JEE mains and advanced and practice solving them, try to enhance speed to answer maximum questions in lesser possible time and finally appear in Jee mains – do well – then appear in JEE Advanced – do well again, It would be better if you would mix the subjects that is do Physics for two-three days, then, may be shift to some topic of Chemistry or Math. This would help keeping things not-exhausting.Now, once you have brushed up a topic, solve some random problems from a book specifically on that topic.Now the most important task during all this is to mark the examples or formulae you find difficult to remember and then keep an eye on IITs/NITs counselling rounds and thus institutions are allotted otherwise there may be second option to visit the official websites of some renowned institutions offering technical studies....to name a few – BHU, Varanasi,...............BITS Pilani,....................JJTU, Jhunjhunu,..................Lovely Professional Uni, Phagwara