Hello

It is great that you want to prepare for cds and afcat while doing graduation. Therefore first you should get familiarized with the syllabus and pattern of exam. You can refer the below link for details

https://competition.careers360.com/articles/cds-exam

https://competition.careers360.com/exams/iaf-afcat

You can then start with basic reasoning and maths practice daily and periodically solving test papers including previous year papers.

Apart from this you should regularly be in touch with national and international happenings through any medium of your preference like news paper, website. Also don't forget to work on your physical strength and stamina as written exam is only the first stage, to get finally selected you have to pass the SSB.

Keep studying