To score good marks in JEE Main paper 2 and NATA your concepts should be clear specially in Mathematics. You can take help of NCERT book to prepare for maths section. 

Practice drawing test. Don't neglect to prepare for aptitude section as it is easy to score good marks in this section. 

You need to have good aptitude and mental ability .

Refer previous year papers to understand the exam pattern and to know the level of the exam and solve sample papers for your practice.

All the best!!