Dear,

Firstly, do the analysis of your complete syllabus and mark the topics that require more concentration. Start preparing the topics from basics. If your basics are clear then only you will be able to solve the high level questions.Proficiency in English is required for clearing the NDA examination. Your English is not only tested in written test but also in interview. You can prepare your GK portion by reading newspapers, magazines, journals, refer books of prominent writers that focus on current affairs, etc. You can refer NCERT books for the subjects. Some good books are by the author RS Aggarwal. Solve past papers, as practice makes you perfect and never giveup. Good luck

Hope this helps!