Here are some of the important tips for the preparation of NDA entrance exam you can prefer:
Syllabus Details: You must have a proper source of the syllabus because a well-prescribed syllabus supports you in making a proper schedule for the examination.
Make A Proper Schedule: You should make a detailed schedule for the examination, those students follow a schedule they may get success in the examination.
Basic Logic Should Be Clear: You must do the analysis of complete syllabus as well as mark the important topics which need concentration.
Practice: Do practise as much you can because Practice will help you in achieving the goal, and a practice is the only key which provides you with an assurance for success in the examination.

Prepare mathematics with the help of the basics of class 9,10,11,12. If you are done with the basics start practicing from a good book.  Be consistent with your preparation.

General Ability Test consist of two sections-English and General Awareness. The English section can be tackled by practicing questions such as error finding, fill in the blanks, Jumbled para, reading Comprehension etc.

For general awareness you need to study the social studies of class 9th and 10th and current affairs. You need to read newspapers for the current affairs.

The weightage of the general awareness section is very high so you need to be more focused on current affairs.

Good Luck!