You can check below strategy to prepare for NDA exam

Mathematics

It will cover topics like Integral Calculus, Differential Equations, Trigonometry, Algebra, Vector Algebra, Matrices and Determinants, Analytical Geometry, Statistics & Probability.

To score good marks in mathematics section your basics should be clear. Make sure you do lot of prctice. Solve as many as MCQs for your practice. 

Work on your time management. Try to increase your speed with efficiency. Solve as many as mock test series. 

General Ability

English

covers topics like vocabulary, grammar and usage and comprehension. This test evaluates the basic command a person has on the language.

To prepare read newspapers daily, Try to learn new word. Your grammar basics should be clear.

You should solve as many as mock test series for English.

GK

The test will comprise six sections: General Science, Indian history, Physics, Geography, Chemistry and Current Events.

Your current affairs should be good. You should be aware of the latest happenings. 

Intelligence and Personality Test

The test usually assesses the candidates for officer-like qualities, which includes sense of responsibility, reacting to situations, social adaptability, team work.

You should concentrate to make your personality. 

It is recommended that you should solve as many as mock test series for your practice to analyse your preparation level at regular interval of time. You should be aware of your strength and weakness and try to work upon them. 

Good Luck!!