Don't be behind your class in terms of content, you don't have to be ahead of your class but you must not fall behind, can't stress this enough especially for subjects like maths or physics. If you're struggling with algebra in your ext 1 classes, really brush up on those Yr 9-10 questions and get comfortable rather than trying to aimlessly complete seemingly hard questions etc.
I would recommend studying ahead in these subjects so when you do learn the content so you feel more familiar with it in class and you can already ask questions you might have; on this note, don't go learning topics way too ahead as a form of study because you can get confused if you go too far, unless your truly fascinated. You don't need to always be ahead and in certain cases its worse off learning content before being taught so try experimenting which works for best for you, simply learning the content at the pace of the class or going ahead - I did a mix of both and it worked out fine.
Thats really the biggest tip I can give because year 11 hasn't posed much new problems that you might've faced in junior years if you've been studious and well prepared, not to say its a cakewalk but it should be reasonable. I enjoyed my prelim year quite a bit, prior to the lockdown of course.. But other than that, best luck.
