Hello.

If you wish to prepare for KVPY exam then first you must be thorough with the syllabus. You have to develop a good understanding of the concerned subjects, Physics, Chemistry, Biology , Mathematics and complete the whole syllabus. Then you have to make a proper study plan and set time to prepare what and when. Then the most important thing is to keep on revising all that you read. But what is going to make a difference is practice. Try solving as much questions and give as many mock tests as you can. Only that will make you more through with the course.

Now to answer your second question, it is better to go for NCERT books Aa they give a simpler and easier understanding of the concepts.