Hey mate, Sydney harbour has great squidding when in a boat as I've learnt, I haven't been land based in Sydney harbour but I'm sure there's squid all throughout the harbour. Just try and find weed bed and places around rocks if land based and or boat based. And as you can see on my pic, you can catch squid up along the beaches as well!
My preferred jigs is yamashita, no particular reason why, but dads been using them forever and I guess it runs in the family.
Casting out and letting it sink and then a flick or two of the rod is my preferred technique for squidding, after one flick