Hello greetings 

 Scoring good marks in maths paper in CBSE is not a difficult task even I know many of my friends who were unable to solve the problems till end but they have written something and got good marks therefore apart from preparation you should take some time to prepare for the completing test in 3 hours because the paper in CBSE mathematics is often lengthy and difficult questions come which runs into you therefore it is not that you leave the questions which are difficult you should attempt all the questions within the time limit that is 3 hours therefore the practice is very essential to complete the paper within 3 hours and one most important thing is that do not skip any questions write at least something which is related to that even though you are unable to crack the conceptual part of the question

Hope this helps all the best