Hi, i did all 3 subjects u mentioned. Based on my experience, to really be successful wrote learning should be a prerequisite. You should already be a good wrote learner and train your memory to efficiently study all the textbook material according to dotpoints for chem and phys, and the general terms and definitions listed on eco syllabus.
That being said you also need to know how to apply the concepts you have learned and select the best pieces of information to answer the question as efficiently as possible, like nightweaver mentioned.
Textbooks i recommend for Chem are "conquering chemistry" and "surfing chemistry" the rest are crap IMO like Dotpoint and the school one i got handed which i forgot its name -.-
i purchased dotpoint chem for $6 off a 2011 school leaver and never used it all year.
For Phys, "Jacaranda" is key, i heard "In 2 Physic" is really good to, although i never used it, my friend from Ruse said it is good.
For Eco, " Tim Ridley" is my favourite, the "Bulmer Updated Economics" is more in depth and should be purchased later in the year when you have mastered the concepts, they are also released twice a year so u should purchase during the time before trials when they hav the budget discussion."Tim Dixon" is my school issue and it's probably very good to have side by side with Ridley when creating notes.
Anyways, try and get a copy of the textbooks above and use all of them to write your dotpoints for ea subject, gl all the best.