Hello Aspirant,


I can tell you that its not a very tuff task and you just need to have focus and determination.Commerce is all about understanding.You have to understand each and every things you read and solve.
Best books :
Accounts : T.S Grewal is best.
BSt : Poonam gandhi
Economics : S. Chand (macro/micro) + NCERT

For accounts its very simple as you just have to solve more and more questions as you can.
For Bst you have to go through and understand each and every paragraph and learn important points
For ECO you have to work hard as you will have to understand as well as solve the question.
All i can say is that you just have to pay attention and focus on what you are studying.
All the best.

I hope this helps.