You can refer below books for CDS preparation:

Mathematics:

1.CDS pathfinder book
2.R.S Agarwal

English:

1.R Gupta CDS book
2.CDS pathfinder book
3.Word Power Made Easy : Norman Lewis

General Knowledge:

1.Geography & History: NCERT (Std 6th-12th)
2.Polity: M laxmikant
3.Economy: NCERT (11th-12th)
4.International relations/events/diplomacy: Pratiyogita Darpan, The Hindu.

Science:

NCERT (7th-10th), few topics from 11th & 12th

You should solve previous years papers of CDS also.