You need to cover the complete syllabus of the CBSE exam, to get success in the examination, there is nothing like to concentrate at any particular subjects. The complete syllabus proscribed by the CBSE should be covered. Following are some tips which will help you in cracking the examination:

Initially read the entire book
Also revise graphs and specially diagrams.
Understand applications of the various concepts
Practice numerical questions in addition to theory questions.
Create a study schedule focusing on topics which have more weightage
Attempt sample papers/previous year papers
Practice writing questions point-wise to score more during your exam.
Read and understand the concept before trying to answer questions