hi rishab,
since i hav qualified jee, i can tell u one thing dat usually topics of 12th class is relatively easier compratively to topics of 11th......
In 12th topics , i wud suggest u dat modern physics is d most easiest topic in iit jee and u can score very high as its weightage is also good so if u can score in this topic den u r always better placed ,,,,,after this i wud suggest dat waves and simple harmonic motion r some easy topics from class 11, again for 12th ,magnetism & current r scoring topics..........
For math, calculus is the most easiest nd scoring topic in jee as it posses a high weightage nd solving questions from dese topic is very less time consuming,,,,Also, vectors nd 3 D are very much scoring topics.........
In chemistry , i wud suggest u to just learn the ncert book specially for inorganic part as if u just remember as many things den u can score at a very fast rate nd this will save ur time for other questions.........for organic , i wud tell u to just remember d named rxns given in d book.....Also i wud suggest to do proper time to atomic structure as dis is a very high scoring topic from 11th chemistry...
Hopefully , dis will help u in ur exam....
with regards
pratham