CBSE 12th

It's great that you know what you want, now there is this point which makes sense, but isn't said very often. Scoring 90% in board is easy, as the papers are made (80-90%) out of previous five year questions. So, if you can I'll suggest you buy previous five year book now and don't wait for next Jan for it. There are books that covers question asked chapter wise, go for it. Before and after getting a chapter done in class, coaching, yourself which ever place you learn and can say I studied it properly, come back home take day in weekend and see the questions and figure out like 10-15 points or theorem or formula that the questions in Exam are based on. I don't remember the exact chapter number but I guess its 13-14 chapters so, around 170-180 points. That's is the key for all subject all boards. Now if you don't have the best resource, happen all the time, go search 'NPTEL' the professors of IITs teach physics chemistry and Maths there. It's simple and extremely good. And, since you have declared that your physics is bad, Don't Practice, try to analyses why is it happening and Google question that comes to your mind for 1 week, you'll see the difference.