Dear aspirant, for preperation of any exam practice is the key.Make a timetable topic wise and before that you should go through the syllabus carefully and mark your weak point, for better preperation of english start reading english newspaper on daily basis that will help you to stay updated as well. Start from basics that is class 6th to 12th school books should be practised thoroughly, they help alot. You may refer to the link for more books and how to prepare a proper timetable

https://competition.careers360.com/articles/how-to-prepare-for-nda

Hope it helps.

All the best:)