Hello Mukesh, 

To obtain 99 percentile in april jee mains, you have to obtain approx. 200+ marks. It is not easy  to obtain 200+ marks, for this look at these points and follow the given steps :

Solve more sample papers and previous years question papers. Learn all  basic concepts and formulae. Ncert chemistry is just like a bible, learnnt them. Solve at least thirty questions of mathematics  per day in a given time. Take timed test series. Revision is most important, revise properly. 

Good luck...