Well if you've caught Breaksea you're on the right kind of ground, depth sounds ok you honestly just need some luck. Look for hard flat coral that's where I've caught most my bangers. And mix it up, biggest Dhue I've caught was on a Mulie.

Try jigs as well as bait. Don't give up it will happen. 

• Small hard lumps (fish stuff as little as 0.5-1.0m variation off bottom) are generally less fished often hold good dhuies. I haven't had a lot of luck catching dhuies in broken rubbley ground (i.e. good Baldie areas). 
• Bottom meat or other large jigs are great for minimising pickers and getting the bigger fish. Even if you leave a 150g bottom meat dredging along the bottom in the rod holder while you actively fish with somthing else.
• Fish big baits if you want dhuies. Wrasse or Srg Baker fillets, large squid whole or a big occy leg are my go to baits. 
• I've caught a lot of dhuies in the middle of the day so don't stress too much about the 'early bite' though having said that, it's usually more productive in the morning.
• Don't worry about water depth too much. I'll fish anything between 20 - 100 if it looks good on the sounder. 

I used to target Dhuie's out in the deeper grounds off Mindarie, but have found way more reliable and consistent catches in the 6 to 10mtr range out of Mindarie and really not that far out.
I change my spots each trip and will usually anchor off to the side of a non descript simple lump or drop off.
Burley pretty hard to start and if the skippy come in pretty quickly I will taper off and use the berley basket on the bottom and use that pretty hard.
I like a change of tide that happens just after dark and will usually coincide everything i do around a change of tide, I can kick back for three hours and the bite usually only happens for 10mins and maybe another hour after that I will get another 5min bite. I very rarely get fish every 10 or 15 minutes so it's imperitive I have everything setup correctly for that quick bite time.
I always use fresh squid that I catch at Obstacle before I head out and setup, I use whole squid unweighted with the hooks berried (just my preference), if there is a current I will use a pretty small ball sinker to get past any annoying skippy, it is really easy to tell a Dhu bite from a snapper and tend to let them have a little run before I set the hooks - Dhuie's tend to mouth a bait and snapper grab and run that I have found in shallow water.
I never leave the baits on the bottom as this keeps the unwanted species to a minimum and usually set at around 1 to 2 mtrs off the bottom depending on current - some days the current will just throw everything out the window, so adapt to it.
That's about it, you can use this technique anywhere along the coast and adapt to your style.
I also tend to find the closer I am to a lump I will get dhuie's and the snapper will tend to be in the sand.
Hope this helps
Scotty

 Without knowing your sounder:

http://fishwrecked.com/forum/587-tm260-dhu-shot-50m

Same as you, it took me years to come back with something decent. Now I've (semi) mastered dhufish ID on the sounder and jigging, I can't catch much else!! I get the odd pinky, but it's dhu or bust on the jigs I use.. Oh Sgt Bakers, I get them.... And sambos.. dammit, sharks too..... And tuna, but them only on blue and silver jigs mid water on the way up!!   

For me I fish the sounder. I don't do long drifts, I just drop on the spot. Give it 2 or 3 drifts then move on if I get nothing.. 

Thing in my books. Doesn’t mater to a degree what type. Once you learn to read and use it. Fish is the easy bit

Great advice by Rob and should have mentioned the placcies, soft plastics can be a hell of alot more fun and just require patience and persistence but the hookups are ALOT of fun.

If you see a 5m Seafarer then avoid the ground that boat is working