Question

i have to go for iit how should i study

Answer 1

work hard, practice as many problems as you can. Follow some standard books. During practicing numericals, start from some basic problems and solve till iit level and beyond.
Try to clear concepts because these exams are based on concepts.
Try to solve problems in very less time. Try to find shortcuts for some specific numericals and concepts.
Don't loose hope. Do not get demotivated. If you get demotivated, watch some motivational videos.
And lastly, stay healthy, sleep at least 6hrs. Inhale some healthy foods. Don't consume junk foods.
Meditate every morning to increase concentration in studies and for effective studies.
You may get some extra knowledge from others (better than me), I don't know it will help you or not.
But still I have shared some of my own experiences. I gave jee exams this year. But I could not clear jee(advanced).
And now I have realized my mistake which did not let me to clear iit-jee

Finally

All the best for your iit-jee and for other entrance exams...