I guess the first thing I'm going to address is that this is a long-term goal and this requires long-term study. Don't think about this all needing to be done in the holidays. You need to study consistently throughout the school year. So don't go burning yourself out in the holidays. Otherwise, you'll only fall behind!
So what should you be doing?
Take good notes Whatever your teacher writes on the board, you should too. I've seen this too often in classes where kids just don't bother taking notes or even opening their books for that matter. If your teacher is taking the time to write a board full (or several) of notes, it's probably important. And you know what that means? It's probably going to be on the exam. Now what I find immensely useful is annotating these notes too. You'll probably find that whatever your teacher writes about they will also spend time talking about it. Write some of their commentary down; it's extremely useful to have their own personal thoughts and ideas written down for you to refer to later. So now that you have all these notes, what do you do with them? You guessed it... you're going to summarise them. Ideally, you will do this at the end of every week. This will not only help you consolidate your knowledge, but give you an extremely useful set of notes at the end of the semester.
As for organisation, you should be dating and giving a title to all the notes you take in class. This helps with keeping a personal record of everything that's been touched upon thus far and can help you with creating your set of notes at the end of the week if you wish to do so chronologically. Now, as a not so organised person, I'll admit that what I'm going to mention next; I've never actually done. But I know people who swear by this method and many academics agree that it is one of the best note-taking method. So what method is this you ask?

It's the
Cornell Method. I'll add a template of this at the end if you're interested but basically, you rule up your page leaving a margin to the left of the page and the bottom. The left side is where you write down and key words or questions. At the top of the page you'll give it a heading (and date!) and in the middle you'll take notes as usual. So what's that bottom section for? Summarising. And while I've never used this method, I've got to say it sounds very useful and is definitely something that should be tried. (Note to self

)
Resources, revision, and reviewResources are essential. You need to make these yourself. They'll help consolidate your knowledge while you're making them and they'll continue to help feed you information after that. As mentioned earlier, you should summarise your notes at the end of each week. In the end, you'll have a stack of condensed notes. But you'll need a few little things on the side. Mind maps are simple, short, and to the point. You shouldn't put to much on these, they're really just there to jog your memory. Likewise, flashcards are incredibly useful and you can practise with these anywhere. I like making physical copies and digital copies (Quizlet is a good app for this). But writing things out really helps me, if this isn't you don't waste your time making both. Just choose one and start utilising them.
Revision needs to be consistent. This means you shouldn't only be revising when you have a sac coming up. With enough resources, revision will be easy. How much time you dedicate this will depend on you and how much time you think you'll need. For me personally, for one subject I will go through the flashcards once or twice a day. And to add onto the flashcards and how you should use them... Have two piles. The first pile should be for cards you have memorised and/or know well. The second pile should be for the cards you find yourself pausing on, or maybe you know you're just not that confident with them even if you have memorised them. The second pile you should obviously pay more attention to. But don't disregard that first pile. You still need to practise them (daily even) but less. You might go through that first pile once, and the second twice a day.
Review your class notes everyday. A lot of people don't tend to do this but research has shown that reviewing new material within 24 hours of hearing it increases your retention of the material by 60%. If you do this now, it means less time furiously studying during exams. So it's extremely beneficial. And it doesn't need to be long. Spend 30 minutes every evening reviewing the days material. That's all you need.
Keep up on your work and any required readingIf you're not completing enough work in class it's important you're catching up with this outside of school. Don't fall behind because this will risk your performance in exams/sacs. Some teachers will help you keep up to date but others won't so it's important you're aware of where you're at versus the class. As for reading, some teachers won't give out reading assignments. Instead, they will expect you to go to your textbook for the reading related to the material covered in class. Ever heard people say they never use their textbooks? Well that's why. So take the initiative.
Involve yourself in classInvolve yourself in class discussions. Be corrected and correct other people. It's the only way to learn from yours and others' mistakes. If your class includes group activities, participate as much as you can. This is the time for you to apply all that theory and knowledge you've learnt thus far. And remember to ask questions if you're confused because leaving it will only make you more confused! And if you find speaking in class a little nerve-racking, talk to a small group of students you're comfortable with or see your teacher after class to have a discussion and address any concerns you might have.
Going to leave this here for now, but let me know if there's something specific you need help with!
