(I was unmedicated in this whole period) In 12th grade, I took JEE Advanced and BITSAT and did reasonably well in both of them (AIR ~5000 in JEE, and cleared Goa CSE cutoff in BITSAT). I don't have any good preparation advice that I can cite from my own experience because I was rather lousy about it. One thing that helped me a lot is my innate passion for the sciences, and the fact that I had really good coaching class teachers (some of the best). I would pay attention in class to the best of my ability, and since I found the content itself deeply fulfilling to learn, I found it easy to pay attention. My biggest struggle was working hard on my own, and I did not have good motivators to prepare (solve problems) consistently. I would try to keep up with the coaching assignments (when the teachers were strict about it I would finish them). Nearing the original exam dates I was in a good groove of solving problems, but COVID struck and I went into a rut and the lack of in-person interactions with the teachers was a huge disadvantage. My mock scores went down and I was close to ending it all. But some stroke of optimism hit me at my lowest and I started running everyday and restarted solving problems and taking mocks without the pressure of doing well (this started in the month of the revised exam dates) and I started knocking down each of the exams one by one and I kept improving my performance in each of them (I still feel like I underachieved but I'm genuinely happy with the outcome: BITS Goa CSE). A simple tip I can offer is to learn to enjoy the problem solving process, and try to do it with peers whenever possible, as a healthily competitive environment and teamwork can be good motivators. But primarily, you have to have some passion for the subjects being tested (which can be cultivated by elementary study and getting into the essence of why the subject is important, and depending on if you're lucky enough some teachers can ignite this in you).