Ive been to these spots many times with minimum success, I do have a few tips for you though.
Get there early as the other guy said
Check the wind before you go, being right at the point 35km 45km gusts are common, fishing near kyeemah boat ramp can provide a bit more releif
Take a couple of rods, the big fish there are very used to seeing big lures and baits, you will be suprised how many times people will have success on bream gear
Check out IndoSydneyFishing youtube channel, I have fished with him a few times and he frequents this area. A lot of land based kings and trevs.
Sadly I have to travel and hour each way to get there (thats assuming you dont get caught in the airport traffic) coming home empty handed isnt fun.