Okay - I suggest going on in year 12 with a high number of units, such as 13 or 14, so you have the option of dropping or picking up a subject when it comes to year 12. So, choose English Ext I and Maths Ext I, and see how you travel with the course and work and see how much you like it.
If English isn't really your strong point, just bear with the Ext until it becomes unbearable, or challenge yourself with it, but I would recommend choosing subjects which aren't as reliant on English as (for instance,) History is. So Sciences - Biology or Earth and Environmental and Senior Science. Chemistry is super picky about the language/terminology, so I personally wouldn't recommend... Try Physics, because it's not as English based but if you haven't done it before be cautious. Geography's alright, and if you're looking for a relatively easy (although heavy content subject, the concepts are basic,) Business Studies is the perfect bludge subject.
It's literally impossible to "fail" the HSC, and if you're hardworking you should be fine.
So:
English Ext I
Maths Ext I (try to pick Ext II when the time comes)
Physics
Senior Science
Geography
To make up to 14 units:
Business Studies
Earth and Environmental Science
Chemistry
Hope I've helped =] Good luck! ^^