I would suggest you to go through the below tips -

1. Schedule your study plan smartly - For good preparation, it is necessary to have a smart study plan because it leads to manage your time and NDA syllabus efficiently and properly.

2. Basics should be strong and clear - If your basics are clear then only you are able to solve the high level questions.

3. Concentrate on GK and English - Proficiency in English is required for clearing the NDA examination and you can prepare well for GK portion by reading newspapers, magazines, journals, refer books of prominent writers that focus on current affairs, etc.

4. Preparation Material - It is very important to choose the perfect study material for your preparation because there are so many books available in the market so it is advisable to choose the standard books which are easy to understand and which make all your concepts clear.

5. Solve Sample papers and previous year papers - By solving previous year questions, your speed will be enhanced as well as you will get the idea about the NDA exam pattern of the examination and difficulty level of the questions asked in the examination and once you are done with this, you can go for online mock papers as well because these will be teaching you time management skills along with you can easily know what all weak areas you are having and where all you need to work hard.

Hope this helps!!!