Class 11 is very different and complex as compared to previous classes, so I’d suggest you to be regular with your studies.
Be present in class, physically and mentally. Keep track of what’s being taught and go home and revise those topics. I won’t suggest books because other people answering might do that for you but also because not all books recommended by people work out for everybody. For eg, I usually browsed multiple links on Google and kept searching until I found the page which was easy to understand and gave me clear cut definitions and examples for a certain concept. So use whichever source is more helpful.