You do need a good grounding in the basics as Slide Rule said.
1. Make sure you know ALL the required formulae. Get hold of the syllabus @
http://www.boardofstudies.nsw.edu.au and make sure you've covered
everything
2. Once you know all the formulae, it's time to apply them to questions from your textbook...if there is just one thing you don't understand, post a thread on BoS and we'll be happy to help. However, your first port-of-call would of course be your teacher.
3. Continue to practise questions...from textbooks, trial papers, past half-yearlies and topic tests etc.
4. If you find that some exercises are too easy, then ask your teacher for more challenging questions...maths in limitless.
Btw. if you can scan a copy of one of your tests and post it on this thread, we can help you to "standardise" it so you have a better understanding of your position.