dear studnt

know the syllabus first

The CDS exam consists of three papers- English, General Awareness and Mathematics.

Clear your concept from basic books

I suggest you to use NCERT BOOKS ,RS Agarwal maths.

For General knowledge, please make a habit of  reading  newspaper daily

For English practice on antonyms and synonym .You can refer to NORMAN LEWIS - word power made easy.

Solve at least five previous years' papers. This will help you identify your level of preparation along with your strengths and weaknesses. Post analysis, you can work on your weaker areas too.

hope it helps

All the best!!!