You have taken a drop to get into top IITs make sure you make it count.

You should be dedicated and work smart to acheive your aim. 

To get admission in Top IITs you need to analyse your previous paper. You should note your strength and weakness and try to work upon them. Don't repeat your mistakes.

You can refer below points for your preparation

1- Brush up your concepts you can take help of NCERT books. 

2- Practice previous year papers

3- You can solve as many as MCQs for your practice and to build up speed and accuracy. You should solve short-answer questions, subjective-type problems and questions based on assertion reasoning to develop deep understanding of the subject.

Important topics you should cover for JEE Advanced are:

    Physics: Mechanics and Electrodynamics are the two most important topics but one should also devote time to Heat, Thermodynamics, Optics and Modern Physics.

    Chemistry: General principles of Organic Chemistry are easy to understand. Numericals of Physical Chemistry are scoring. Inorganic Chemistry has many facts and figures and requires constant revision.

    Mathematics: Master inter-relationship between various topics. Coordinate Geometry and Vectors can help one to solve problems related to complex numbers. Permutation and Combinations help you to solve problems of Probability. Trigonometry and Calculus again help one to solve all types of problems.