India

I am not going to go into the details regarding time management, schedule, etc. I will rather focus on some secrets most aspirants miss out, know yourself. Not everyone is a born genius. It's important to know where you stand, after starting preparation, it will hardly take 3 months to get to know yourself. You might be a 360/360 person. A god.
250/360 person, an average person who can get into IIT.
180/360 person. You need to work a little harder.
100/360 person. Zip up and work hard. Never keep a backlog. I once left a topic in chemical bonding in class 11th to study later. Well I still haven't covered it after 4 years into IIT. Have a study pattern. Studying without a plan is a sin in such competitive exams. Make a plan. In my days, I made a brief plan, used a chart paper, divided it into 3 halves and made a plan. For more of it, have a look: Vichitra Zawar's answer to How can I study for 10+ hours a day without getting depressed and how can I make myself get used to it? Study smart. I used to study my boring part when I was fresh in the morning, mugging part (Chemistry), Physics in the evening and Maths being the most exciting at night. Keep revising. Revise what you've studied on Sunday. It's a great habit. Never solve problems in rough and throw your solved work. Keep it fair. It will be helpful in gaining confidence and further reference. Maintain a hobby. You always need something to distract yourself on this journey. Everybody studies the same amount of syllabus, and smart people excel.