TO score 90% in chem or even more in board one should read ncert thoroughly . Dont focus on anything just ncert and its each and every question. instead of focusing on any other book just read and solve ncert as many times as possible .
if you are taking tuition/ coaching then there u can learn the concept of organic chemistry from there only. Understanding of organic chem is quite important and if u are not taking any tuition then u can refer book named as solomon fryhle organic chemistry ( but only refer some concept , don’t start reading each and every concept from it).
Don’t take those short chapter like biomolecules, polymers, surface chem and chem in everyday life lightly as many short questions are being asked from these topics which boosts up ur confidence during the examination when u can handle those 1 markers.
Lastly , present ur answer sheet in a very neat manner. write the rxns of organic in very neat and clean manner leaving good amount of space. solve numericals in steps and in neat and clean manner. if u need to cut anything just strike it once don’t scribble to cut any mistake.Keep all this small things in mind as ur answer sheet is your reflection to the teacher who is checking ur paper.