To Boost your confidence, I would suggest you to do practise as much you can & Attempt the Mock test, It will give you an almost real experience of how the examination will be. By solving mock tests, you will be able to work on time management while at the same time understanding the question paper pattern and also analyze your storng & weak areas.

Do Revision- While studying it is important to revise those topics which has already been studied. It is advised that each day, a certain amount of time should be divided for revision purposes. Revision is very important as the syllabus is quite vast and all topics have similar importance level.

As you told that you are studying class 12th, Your class 11th & 12th syllabus will help you to cover the exam syllabus, Go through with NCERT books it will help you to clear your basis concept then you can prefer the books.

Careers360 has come up with JEE Achievers Preparation package which includes unlimited tests, online 24*7 expert chat facility system, conceptual e-lectures and many more plus points for you. It has a time table feature as per which you will have to choose the exam date and your complete time table will be auto-created as per what topic you should focus on and the amount of time to be given on each topic.

Apart from the above mentioned:The best part is-

In respect to the program mentioned, you can practice the tests any time of the day and that too unlimited, so utilize it to the extent.

There are concept wise lectures, which means you can get your minimal to important concepts cleared and followed with it can give the test and analyse your performance.

Even if you plan to study at 3am, and you face any query, you have online doubt facility system where the experts will help you asap and you don't have to wait till next day.

Further to know more benefits helpful for you, you can check details and proceed from here- https://goo.gl/zTUHWw

Good Luck!