economics is VERY much in the NOW, you need to ensure u know the very latest of figures...although having said that they wont deduct marks if it is like 1 month old or something...just ensure its quite accurate. and memorise numbers!!! eg eco growth, inflation rate, interest rate, etc., but dont go balistic...only the basic ones that are handy to throw in to an essay and make you look smart...
i dont understand wen ppl say plan essays...you SOOOOO do not do that in economics! by all means, take lots of past questions and write plans for em, detailing what you would talk about, and you will see it becomes quite repetitive and similar...but NEVER EVER say...ok i would write this for an inflation essay, this for a blah blah essay coz chances are you'll do better not having 'pre written' essays...(trust me, i learn from experience!!)
since you've got a while till the hsc rite now, ensure that u utilise your teacher to the max...pile up more and more practise essays, and not just the ones he/she gives you...the more you do, the better you'll get...
BTW, the planning process of an essay is vitally important, just as important as the essay itself, since an essay with no direction or scope is useless...practise under time getting a question and planning it...try to go faster and faster...