do past papers, know the syllabus and current affairs, also revise any homework, assignments and make notes on all topics. The BoS rights that a band 6 is capable of doing this:
integrates economic terms, concepts, relationships and theory in a variety of economic contexts
displays superior analysis of the role of economic participants and markets in a variety of economic contexts
uses extensive economic vocabulary and illustrative examples in exposition of problems and policies in a variety of contexts
demonstrates critical judgment and sound reasoning to select, organise, synthesise and evaluate relevant information from a variety of sources
presents excellent explanation and evaluation of the impact of government economic policies in contemporary and hypothetical economic contexts
presents comprehensive application of appropriate mathematical concepts in a variety of economic contexts
produces comprehensive economic arguments to evaluate the consequences of economic problems and issues on economic participants
so initially ensure you incorporate these points in HSC exams and also look into tutoring.