Don't stress too much - year 11 is your year to play around with your subjects, get to know a study routine and get a feeling for year 12. I over thought this before year 11, but coming out of it now i can say at the end it feels like you had just completed any other year. You will have a steep learning curve initially (unless you have applied yourself extremely well years 7 through 10) but after about term 1 you will be find. To be honest I didn't even really stay on top of my workload this year out of sheer laziness.
Now, I will talk about english because the only essay related subject i do is English Advanced:
For your essays i will say practice makes perfect (cliché i know, btw i only do 1 subject in which i produce essays so try and bear with my advice). By the way, if you haven't ever done this, i would recommend trying to get a hold of essays from the previous year in your subjects to see how they tackle them. Try and morph these techniques and ideas into your essays. If your school wont supply you with the previous years essays for whatever reason (even a sample) then you should maybe ask one of your friends who is performing quite well academically (some people are pretty touchy about showing their essays even after it has been assessed). If that fails, look for some online/BOS.
Teachers will want to see a step up in your essays. Now, in english (speaking from experience) you want to know your texts early if you want to ramp up your essays. I have gotten 16/20 in essays this year without so much as reading one page of the text, but i read sparknotes, read online resources and obviously extrapolated quotes here and there. Basically knowing your texts very, very well makes you an absolute boss at essay writing. Look at marking criteria before an examination, do practice essays before exams (heck! i didn't even do one practice essay before my first english examination in term 1).
One thing you will find is the 'brain dump' simply just doesn't cut it in year 11. You need to concisely answer essay questions, making clear reference to the question throughout! You can no longer hide from the question. But don't be alarmed, as long as you have a fairly good thesis (this is not really very hard to develop, after all your arguing your point in an essay and thus you can never really be wrong) answering the question properly should not be too difficult.
BOS is always here to give you help & guidance on any essay questions!
Good luck.