The primary subjects from which questions are asked are,
2. Data Ware House + Data Mining
3. Operating System
4. Data Structures
5. Languages: C++, C, Java
6. Computer Network + Network Security
8. Software Engineering
9. Computer Organization and Microprocessor
One third of the questions are easy only, rest are of moderate level.
Just mug up the basics.
Do not go for any offline material Disha/Arihant or whatever. They are a sheer waste of time and money.
Study resource which I found best and which worked for me : Tutorials_Point website’s pdf
You may not find them all at a single place, so here is the link to all the pdfs : https://drive.google.com/folderview?id=13Qd-vhfd_RO6TsKU97idD4WzAL5jNpJh
Take addaa online test series for mains. Keep practicing through daily IT quizzes from addaa247 app.
Other good (or may be better) websites : San_Foundry, Afffairs Ccloud..
But before doing any question, or attempting any test/quiz, make sure you have gone through the study material thoroughly at least once.
do check out previous year questions of SO IT.
u can find them somewhere in my older posts.