Setting decoys, I use a set up from 3 decoys to 3 doz. Depending on the number in the area, and the hunting pressure. Setting up a few goose decoys....above and out from them, acts as a confidence and a blocker.
I also use to use a "C" or "U" spread....or two groups. The larger group set up wind. Set 2 approx 25-30 or more away from the main spread.....down wind...roughly 15 yrd or slightly closer to shore. This simulates a pair just lit and are swimming in.
Using a pair a pintail and or a few mallards mixed in...or just outside the main black rig....as window dressing. You can use widgeon or some other colorful decoy. Some type of full bodied decoys in and around the water add so much confidence.
Some divers don't hurt, set out to about 40-45 yds are a nice touch..but don't need them.
Some crow decoys near the blind or in the trees is icing on the cake.
In every spread...leave a lot of room, unless using spreads that don't require it. I'm taking and my most successful spread was 7-9 decoys...blacks...and some window dressing.....up wind.
I'm sure you know all about hiding and camo. If you get caught standing outside the blind....and see the birds, hopefully before they seen you...stand still...you may get them to comeback, with some convincing calls.
I've killed ducks hiding behind nothing but a small hand full of tall grass.
Blacks can be super wary one day...and dumb as a post the next. Weather plays a huge factor with them.....I would say even more so then mallards.
In my area.....the blacks never really seem to hang out with geese...so I always kept some distance between them.
Calling. Not near as aggressive as calling mallards. Very subdubed.(sp) A hard comeback call can work....or a fast yak yak yak yak yak. Not neccessarily saying that word. Single quacks can be very deadly. Blacks seem to be most vocal during the early morning hrs or dusk. Sunny days.....you can call way less, and slightly more on cloudy days. When you are in a good storm...calling is almost nil. I had a special field...when an east wind would blow over the trees...and very little calling needed.
On high tides...hit the fields...on super low tides.....stay home...unless you have a sweet spot where they may hang. They seem to hangout in the deeper water when a super low tide occurs.
Obviously...it's all location location location.....but you have to keep it real. As real and natural as possible.
Being here in Illinois, we don't get many chances at them. When I lived in NewBrunswick Canada...blacks were our main duck. From day one...to ice up. They humbled us many many times. If I had ever learned everything about them...I probably would have given up hunting them.
Thanks and good hunting.