Go to the Board of Studies website, download all the past HSC papers with solutions. Do the questions.
See if you can get your hands on a mechanics textbook like Schlenker - Guide to Engineering Mechanics, read through the parts still assessible in the HSC and do the questions.
For mechanics, best method for studying is to just practice doing more questions
See if you can't find some of those CSSA past papers around on the internet. They're okay too.
Also make sure to get enough practice doing engineering drawings (iso, orthogonal and oblique) so that you're comfortable doing them. (If you can find a set of parallel rulers, I'm pretty sure you can bring that to your test, and they help a great deal with isometric and oblique drawings).
Also with mechanics, I found "A Student's Workbook by John Rochford" pretty helpful and concise in terms of learning the procedure of doing the questions.