Hi Diversion90,
If you're doing 150 hrs syllabus, make sure you read this first:
http://www.casa.gov.au/fcl/download/vfras01.pdf
(page1-5)
(ii) after accumulating 5 hours pilot in command cross country time, or achieving the competencies of the
PPL (as specified in the PPL Achievement Record)
• Navigation
• Aircraft Operation, Performance and Flight Planning
• Flight Rules and Air Law.
Since you mentioned you have PPL, I assume you already have 5 hrs PIC x-country time.
I recommend start with MET because CPL MET is 95% identical to PPL MET. If you have PPL already, CPL MET shouldn't take too long to prepare. Difference is CPL MET is heavily based on interpreting weather forecast, so make sure you understand the forecasts at the end of Bob Tait's textbook.
Then, do AirLaw. Some elements mentioned in MET will be covered again in AirLaw, so save you time to study the MET element again. AirLaw also helps you to learn how to find info from AIP, CAO & CAR. These are very important reference for your CPL training.
Then, do Nav. CPL NAV is also very similar to PPL NAV. It covers MET, AirLaw again, so you save a lot of study time. After study Bob Tait's Nav book, I became very confident in using the 1 in 60 during my solo flights.
Then, do AGK and aerody. They're very straight forward and interesting to learn.
Then, when you have plenty time, do Performance. This subject takes a lot of time, normally I can do other subjects in 2 weeks, but with Performance I actually spent 4 weeks. Make sure you spare plenty of time for this one.
Finally, do Human. It's not very difficult and is 99% identical to ATPL Human, so as soon as you have all credit for CPL theory, you can sit the ATPL Human the next day.
Just be careful with Performance, you really need to allow more time for that. Most of my mates under estimate Performance and found time not enough to study this subject. I think Met, Law & Nav are most directly related to your x-country training, so I highly recommend doing them first.
Enjoy your flights!
and study......
p.s. If you're doing NVFR, the Aviation theory centre has a very good NVFR textbook. They also have a very nice initial twin-engine textbook!