Some of the chapters are going to be the most important based on one's strength and weakness; however, for most boards exams, these chapters are going to be of utmost importance.

Following is a general outline of important chapters for various subjects:

Science

Physics:

Electrostatics

Current Electricity

Optics

Modern Physics

Chemistry:

Chemical Kinetics

Electrochemistry

Organic Chemistry: Hydrocarbons, Alcohols, Phenols, and Ethers, Aldehydes, Ketones, and Carboxylic Acids, Amines

Inorganic Chemistry: p-Block Elements, d-Block Elements

Biology:

Reproduction in Organisms

Genetics and Evolution

Biotechnology: Principles and Processes

Mathematics

Algebra: Quadratic Equations, Arithmetic Progressions, Coordinate Geometry

Calculus: Limits, Continuity, Differentiation, Integration, Applications of Derivatives, Applications of Integrals

Trigonometry: Trigonometric Functions, Trigonometric Equations, Trigonometric Ratios

Vector Algebra and 3D Geometry: Vector Algebra, 3D Geometry

Social Science

History: Indian National Movement, World Wars

Geography: India: Physical Geography, Climate, Natural Resources

Civics: Democratic Rights, Fundamental Rights and Duties, Judiciary

Economics: Economic Development, Globalization, Consumer Rights

Remember, though these are the main chapters, a holistic preparation covering all topics would suffice.

For even more specific help, look at the following:

Previous Year Question Papers: Analyze past papers to spot most frequent questions and question patterns.

Syllabus and Exam Pattern: Familiarize yourself with the latest syllabus and exam pattern to prioritize topics accordingly.

Consult Teachers and Mentors: Draw guidance from your teachers to know how much weightage is there to different topics and get any personal advice.

By concentrating on these areas and by regular practice, you may significantly improve your possibility of scoring good marks in the board exams.