Usually cast the jig or placcy ahead of the drift so that it's down the bottom by the time you start working it from above. Most times they get hit on the way down. We fish all depths but 30-40m is ideal imo.

 I swear by paddle tail plastics 5-7 inches and at least 40lb leader. I even caught a 50cm dhuie on a 9 inch eel imitation soft plastic so I'm definitely convinced it's more about finding them than technique. If your plastics are coming back with bite marks it's almost always wrasse and baldchin groper which have smaller mouths and struggle to eat a whole plastic with a decent hook, which brings me to jigs! 
My mate i fish with mostly uses jigs around 100-140gram with twin assists, he catches just as many decent demersals as I do but certainly catches a lot more baldchin groper and snapper that seem to elude me as they seem to just strike at the assist hooks with the skirts on them. I will say having a sharp hook is essential to convert those hits into hookups. Don't let them rust away or stay bent if you got snagged and got free. 
good luck! 

The line angle is a lot more critical when fishing with jigs moreso than plastics. Most plastics will work better with a bit of line angle rather than straight up and down, unless you are just dropping into a school of dhuies. (they will normally smash pretty much anything on the drop, action, presentation really not important)

If you are drifitng (not hovering on fish/ground) plastics can be fished at a larger line angle, even put in the rod holder and let the boat do the work. Jigs will need to be cast ahead of the drift so that you are vertical when it hits the bottom, once line angle gets too severe and it is affecting the action of the jig and your abiltity to impart action then wind up and go again.

Like any fishing, its all about time on the water doing it and working shit out slowly. The most important thing is to be fishing where there are fish.

From the sound of the way you fish, i think plastics are probably your best bet for the moment. A suitable rod and reel with quality braid and leader (i like a couple metres of 50/60lb fluoro) so that you can feel whats going on and get your lure down easily is pretty important too. 

I like 7" Zman jerk shads and also any 6-8" paddletail. Jighead weight is just as critical as what plastic you're fishing. 40-50m I normally use 2 or 3oz, 7/0, 8/0 hook.

 I've just started getting into metal jig's in the last 3 to 5 months as well Sea Goat and have watched countles youtube vids to better educate myself.

And if you watch enough of them it seems most of them get that hit on the way down and on the first drift (well that what appears to happen) and i am yet to see it, so i am not yet convinced there better baits , as when you see the deckie getting hits and catching fish right beside you , it doesnt take long that you switch back to baits as your the one bleeding.

Now as i am new to it, i may not have the right action going on, the right jig wieght go on , I'm not holding my tongue right, i dont know but i will stick at for now as i use soft plastics and really like the hit of the soft plastic, compared to the bite which i think is the addiction to it.

The critical parts i have learned so far is your line needs to be vertical, so that comes down to jig weight selection when drifting, so you need a selection $$$ (no different to soft plastic head weight selection) quicker the drift, heavier the jig, but as light as you can get it for the conditions.

Line class. Thinner the better. I've done alot of fishing and always my go to break strain is 50pound (Dhuie fishing) just is, 80pound leader. And have never researched it at all untill i started this jigging venture. Have never taken any notice of the line classes they use on the fishing shows just go's over the top and straight to the keeper.

But i think theres alot in it when it comes to jigging, gee's there using pe 1.5 to 2.5 jigging in 2 to 300 metres of water. 

Fluro carbin leader, lighter the better 40pound, Only a metre or so   

I've gone down the purchase path of fluttering jig more than the knife style jig and from what i have noticed is, the more frilly bits on the assist hooks appear to catch our Dhuies from my research.

Not sure about double assist, personal opinion is, if your on some narley country there more easier to snag and loose a $25 jig, which with my lack of success so far i'm not necessarily happy about.

Putting action into the jig. Well im still working on that one.

Rod selection? watch enough vids and they seem to make a difference. Dollars start to add up if your not having success. But am happy too if i thought i could out catch anyone on the boat haha.

Like you Sea Goat i'm full of anticipation on my next journey to catch a quality fish on the jig

thanks heaps guys!

just and update....got my first fish on plastic on friday....well kinda....pulled up not 1, but 3 big cutlefish form 50m of water on a red paddletai with 7/0 hookl! lol! go figure... still nothing with scales  tho!