After reading a book or attending a class of physics, maths or chemistry we make notes. First thing we need to note every physics maths formula for iitjee and short concepts for the topic. Most student after doing a topic moves to other topic. This way he starts skipping formulas of last chapter from brain. This leads to invention of a formula book and charts. Here I will discuss the method to make formula book and charts along with its uses. It is as used by me for my exams which lead me to become a topper.
After completion of a chapter carefully enter all formula of maths or physics in separate book. Take all notes and books on the table and start from first formula of the chapter. Write it and also mention its uses also note units and names of variable used in the physics formula. You need to mention which formula is useful if there is more than one case. Also write value of all physics constants. For maths write values where ever needed. You can also take help in making formula sheet from video lectures for iit jee by iitjeemaster.
Also make a chart of formula with same content and paste it to a place where you can watch it again and again. Chemistry needs many charts and that will need extra space to paste them. Paste all that inorganic and organic chemical equations which you think you may loose from brain. Paste formula charts to garden bathroom as well and give it a look every day.
At the teen age memory is not developed to its full potential hence it needs regular touch with the formulas for most of human beings.
Do not write many short formulas as they may not useful and will make an extra burden for memory. Try to solve problems by basic concepts and formulas instead of any short cut or thumb rules. So avoid too many less used formula.
So now if you have made formula books for iit jee maths physics learn to use it. Your first aim before going to solve is to remember all themes for that topic so read and memorize all that you make. Every days until you got all in mind. After that problem solving will be faster and accurate.
Now all your stuff is ready for last time reading as well as for daily use.
Reading all physics and maths formulas just before exam days will make 5-10% marks for you for sure. When I was preparing for IAS exams I had my physics formula bank and after only one day reading of formula I did attempted all problems in physics paper. I passed it three times. This way every student will get immense help in jee preparation.