Since Economics involves significantly different content compared to Year 10 Commerce, there isn't really that much you can do to prepare beforehand, since the Prelim content will be completely new. That being said, before going into Year 11 I took a quick browse through my textbook, in particular Chapter 1: What is economics about? (from Tim Dixon's book). This should give you a good orientation of what you'll be starting out with in the course, and a quick browse through your textbook should give you an idea of what's in store next year.
Have a look through the Economics syllabus also, in particular the Preliminary Course description. That will direct your study next year, and give you an overview of the course.
Other than that, I wouldn't suggest you can do much else as the later content will be unfamiliar. However, if you want a head start just read through the first one or two chapters to orient yourself. When you go back to school next year, you'll be introduced to the content at least, giving you a good head start over those who haven't looked at the content yet.
The Prelim course essentially takes a microeconomic focus of Economics, meaning each topic looks at a different feature/component of the economy and the role it plays in the whole economy. After being introduced to features like the PPF, business cycle, circular flow of income, product/factor markets etc, you'll learn about the role consumers/businesses play in the modern market economy. Then you'll examine how supply and demand work to create a functioning economic market, looking at financial and labour markets in detail. To end the course, you'll study the role the Government plays by intervening in, and regulating, the economy.
This is just a brief summary of the course, and in time you'll learn all of these features (and more), becoming a proficient student of Economics. It seems like you have the passion and drive to succeed, so if you can apply these attributes to your study of Economics I'm sure you'll do well. Apart from a brief reading of your textbook and possibly some online sites, you don't really need to prepare too much before starting the course. You'll be introduced to the content when you return next year anyway. Good luck with your Preliminary studies!
