This is a really hard question to answer, people can only give you certain pointers but becoming productive or efficient is something only you know yourself. That's why I don't want to refrain from giving you direct advice since I don't want you finding out the techniques don't work for you and I wasted your time.
See what you did good this year, remember the times you were hard working and you put your head down and actually studied, even if it was 10 mins. Apply those techniques again and try to develop a routine. Pomodoro technique is a famous one for beating procrastination and it certainly is effective for most people but certain people don't find it beneficial - and this is the same case for other techniques. You just have to experiment, and you have the yearly holidays to do so, so don't sweat.
Also recognise that productivity is always fluctuating, you're going to be way more efficient in some days and way less efficient on another day and that's completely normal. What I'd say is that you would want to start working ahead of your peers or the class, now I'm not saying start studying Year 12 content and read every Shakespearean play known to man, but rather just get a slight headstart such as going over the first term content briefly, you'll find that you'll be more engaged and from it become more productive because you compensate the days where you're being lazy by making up for it before (if that makes sense).
Year 11 was extremely chill for me, you'll pull all nighters for sure but you should be fine for the most part. Just enjoy the year. All the best.
