Just finished the HSC and can fill some things and tips in:
Economics - enjoyable, interesting. Reading newspapers and knowing things outside the textbook will get you those extra marks in the exams! Writing essays is an important skill (thankfully, u don't have to be good in English -shudders- to be able to do this well).
Business studies - dropped it. Pretty boring for me, but might interest some people. Problem is the HSC course often rehashes the content in Preliminary course, only in a greater detail, but it will still be dull... Writing essays and business reports is necessary.
Biology - didn't do it, but you should be prepared to cut open dead animals
Advanced English (shudders) - In exams, prepare to feel pain in your fingers as you write 3 essays in 2 hours. But remember: quality is better than quantity (although if you can achieve both, you'll do heaps well)! My friend only wrote 3 pages and he got the top mark for that question (18/20).
Always think outside the square! This is the most important skill you need for this subject. With today's syllabus, you must be able to broaden you perspective on each module. Read sources not given by teachers and do some research to gain those extra marks, and these marks are extremely important since they separate the top students from the bottom.
And never ever memorise essays. You may prepare them, but never memorise! Coz if you do, once you forget even a sentence in an exam, you can hit a brick wall.
Finally, don't plagiarise essays from past HSC in your exams. Teachers know some of those exemplars on the net or school server, so you don't want to risk it. Do get some of their ideas though. They're there for a reason.
But I guess since you're doing ext 1 english, you should do well in advanced english. Anyway, hope this helps.