You can refer to NCERT books to prepare for CDS exam.

For polity you can go for M laxmikant.

For English R Gupta CDS book, Word Power Made Easy : Norman Lewis

For Mathematics you can go for R.S Aggarwal

It is recommended that you should refer previous year papers to understand the exam pattern and level of the exam and mock rest series for your practice.

All the best for your exam and preparation!!