I scored 60% in class 11.Currently I am in class 12. I want to crack Jee Mains as well as wants to score more than 90% in class12 CBSE board.How can I do this through self-study.

You need to work hard so start your preparation.
To score good marks in jee-main you should be aware of all the concepts for that 5-6 hour study is important.
Now to combine board with it do a thing whenever you see any formula try to find its derivation that can be asked in jee