hey man. mm. personally, i've found spearing decent fish from a perth shore dive to be quite difficult. a dive at burns beach will tell you a lot, because, despite being a protected zone, there aren't a lot of spear worthy fish in it. the odd king george or flathead being two exceptions.
there are a few decent spots around two rocks, where you might get lucky and snag a decent breaksea or (if you're really lucky) queenie, but i've learnt not to get my hopes up.
crays are a bit easier to come by, and abs, and it's almost possible to snag a dhuie from the beach (almost) just before the demersal ban, when they come in to about 13m in some spots. i've also seen some undersize baldies on occasion, so you mgiht get lucky there too.
but that being said, i'm mostly in the same category as yourself, a beginner looking for better spots. there are some really good looking spots to practice your diving around perth. be careful showing your speargun around burns, unless you don't mind everyone glaring. same goes for the area behind yanchep lagoon (which has a deep ledge right where the waves break, which can be quite dangerous). leeman's landing in two rocks is another good practice spot, if none too fruitful and north of there is durr's, a good few kms of shallow reef. all those spots are rarely deeper than 5m.
freo, on the outside of the harbour (rous head) is a bit deeper, 6 or 7m, but again scarce on the scaly side of things. mosman and cottesloe beaches have some good dives, but are protected, and i'm not sure about north beach as far as its protection status goes, but that's a good dive too.
anyways, let me know how you go (or if you find any good spots!
).