CBSE 10th

Make a study timetable - Dedicate 7-9 hours to studies in the initial stages of preparation (assuming no previous coaching). Try as hard as possible to stick to this timetable. Also, give some time to physical activity as well as to any particular interest (such as coding). This will give you the power to work hard, and keep yourself energised in the process.
Define your study material- Stick to a particular set of books, coaching materials, problem sets, etc. Do not deviate from these at all throughout your preparation. This process will give you confidence to believe in your decisions. Believe me, people will try to drag you into studying different books.
Start Working- Begin with topics in Maths and Physics such as Theory of Equations, Straight Lines, Conic Sections, Kinematics and Newton's Laws. Start studying the theory, try to think critically and efficiently while solving problems, or in general work to build a psyche towards problem solving. Develop a Positive Attitude- In the duration of your preparation, you are bound to make plenty of mistakes, find difficult concepts and feel exhausted. Be positive always, never let the thought, will I be able to make it enter your head. Learn from your mistakes, work hard to grasp the concepts and place them in your mind. Just keep a never-say-die attitude always.
Avoid Chit-Chat- Generally avoid discussions regarding concepts or topics (Plenty of time for that later). If you have any doubt, go straight to your teacher and ask him/her to clarify it for you. This is because a misconception can easily creep into your head, with you never knowing it. It happens due to peer pressure, and you are not at fault. But the principle which is most useful is:
Practice the art of doing the right thing at the right time. This will keep your morale up, boost your confidence, and enhance your ability to perform under pressure. Developing these will keep you on track once preparation starts.