Hey mate,
I can't speak for everyone but I generally dive in the winter, weather permitting. Quite often in the winter, down south here in Perth and surrounds doesn't produce the best visibility in my experience. Often I end up heading down to Margaret River and surrounds. Problem with this is the effect that swell can have on dive grounds, making it very dangerous. It's hard to get in to the water off the rocks without getting hurt, losing equipment or getting swept away. Getting out is even harder. But weather permitting, I do dive in winter. Since you're up in Perth, I recommend that you go and join a club. There are two main options that I know about:
WAUC (wa undersea)
Blue water freedivers of wa.
If you're ever in Bunbury or surrounds, hit me up for a dive.
Thanks,
Rock Shooter