I am in 12th class and want to know the way of preparation these exams.

							
hey,
if you are aiming for cracking JEE/AIEEE it would be necessary that you should start preparing for the exam because very less time is left from the exam.
Make sure keep on revising all of the thing that you have studied so far along with what you are studing during 12 class.
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So it is very important that you start doing you revision work daily but make sure that you first complete your daily work then go for revision. At this time 1 hour per day for revision is sufficient, along with your regular studies.
And slowly and slowly increase the no of hours for revision as the burden from your coaching come down.
Make sure you revise all the important concept in each subject.
for chemistry, specialy for organic and inorganic, make sure that you keep on revising the course, mainly reagents, otherwise it will create a big problem at the end.
these are some books which will help you in strongening you concepts
http://www.askiitians.com/Important-books-iit-jee.aspx