Hii Prabhat!

Let me tell you that no study method is wrong or right. It's just about what suits you. If you feel making notes at the side of topics in the book itself is good, go for it. And S.L Arora is a good book indeed. But, make sure that while making notes, you di t create a mess in the page. Keep it clear and less sophisticated. This will help you revise faster where you don't have need to find for some points. And it would be better if you prepare side notes too in a small pocket diary. This will helps you revise even better in less time. And most importantly, be confident on your study strategy or change it. Hope this helps.

Good luck!

Dear aspirant,

I also used to write extra points on the books like you and it helped me to understand question and write answer in detail. But it had one drawback that these books not become handy when you want to do a quick revision. So with my experience I would advice you that it is not enogh to write extra point on the book alone ,you should also prepare short notes  for your self while studying so that when you want to do revision it becomes handy and easy to do.