Hello Pravin, To clear NDA, things that are needed to be done

- last 10year question papers for the better idea of NDA Exam.

- Proper time management while solving questions.

- Solve sample paper as much as you can.

- Improve your English. Start reading a newspaper daily and make it a regular habit to watch news on TV. Also brush up your Grammar skills. 

- Identify your weak subjects and start working on them so that you gain a stronghold.

- As there would be negative marking, try to prepare yourself in such a manner that you do not have to make any guesses in the examination hall. It is best to answer only if you are very sure of the answer. Guesses are not going to pay here.

- Last but not the least, start thinking and behaving like an officer.

All the best