O level self preparation :
There are two types of books in the market. Indian writers' and US/EU writers.
Indian writers' books
These books are favored by our schools and coaching centers as it puts all the explaining up to the teacher. And focuses on rot memorization for the students. There's not much to understand, other than practice and memorize the rules.
On the other hand US/EU books
- Focus on understanding the concept
If you are focused on self learning then buy these books instead of the Indian ones. You will learn a lot.
FAQ : "Do I need a teacher or coaching?"
Not really if you can read the book and understand it. Teacher will basically translate the book in Bengali and repeat it to you. That's as much redundant as it can be.
"So when do we need a coaching?"
When you need some push from a figure in authority to force yourself to read and learn. Learning is a painful process and not everyone enjoys it.
You might enjoy a few subjects while not enjoying some other but you have to sit for those exams regardless. Take coaching for those.