hey! beatroot has pretty much hit the nail on the head - past papers! past papers! past papers! i'm not going to sugarcoat it and say it's not time consuming, but it is, and the more practice you do, the better you'll get. also make sure to hand them up to your teacher. :-)
ww1 is a source-based study, so interpretation of sources is a huge part of this section. once again, practice really helps. the more you do, the better! you have ww1 notes, awesome! focus on memorising detail, because heaps of the questions ask for your own knowledge, and detail is a huge part of that. there's some guide out there here on AN which gives a quick rundown of how to memorise detail, and if you check out the notes tab, there's a detail table created by susie, the modern lecturer here!
as for your other options, i highly recommend doing your notes throughout the year. sure, it's really tedious, but doing this will ensure you don't have to write notes as your study before an exam. this way, when you're doing past papers closer to the exam, you have your notes already done to refer to. it's also really satisfying to finish writing a set of notes :-)
also, i can't emphasise how good teaching others and answering questions here. participating on the forums and answering your friends' questions is a really great way to study because you're actually applying your knowledge.
hope this helps :-) modern is such a great subject - you'll have an absolute ball this term and the coming year!
best of luck for year 12,
fantasticbeasts