People have used duck decoys to hunt ducks for thousands of years. Most likely, you will need to use them as well in order to bring home ducks for the dinner table.
Native Americans 2000 years ago made floating decoys out of cattails and bulrushes to lure ducks, geese and other game within range of their nets, or bows and arrows. Their decoys were relatively simple in design and were a perfect complement to the strong concealment and other hunting skills these natural hunters possessed.
Today, most hunters use duck decoys made of plastic or other synthetic materials. A few will still use wooden decoys, for aesthetic or historical reasons. Mostly, however, the lighter the better - plastic doesn't weigh as much as wood.
How many decoys do you need? Well, it depends on the type of water you hunt. Large, open water tends to require more decoys to draw ducks' attention. It's not uncommon to see decoy spreads of 8-12 dozen in the open waters of the Great Lakes, the bays of the Atlantic and Pacific Oceans and the Gulf of Mexico, as well as other large bodies. Smaller water bodies - farm and ranch ponds, creeks, flooded timber areas, small inlets of larger bodies - require fewer decoys.
A good rule of thumb is one full, backpack-style decoy bag per hunter. In most hunting situations, this will be plenty - probably even more than enough. And nothing says you have to set them all out.
Late in the season when ducks have been shot at up and down the flyway over every duck decoy there is, less is more. Two to three dozen magnum decoys generously spread on an open water body will do the trick. On a small pond or creek, a dozen or so regular decoys, or even small teal decoys will work just fine.
1. Match duck decoys to the species you are hunting (don't use mallard dekes to hunt brant or eiders).
That being said, large varieties of ducks will decoy to a mix of mallards, pintail, widgeon or teal decoys, or any decoys that are generally drab brown or green. My redneck cousins used to hunt the Little Missouri River bottoms with decoys made of half-gallon plastic milk jugs they spray-painted in swirly camo colors. Ducks came gliding in to them like crazy.
2. Use motion decoys strategically. I know I'm going against the grain here, but in my experience, motion decoys don't add significant numbers of ducks to the strap except in one condition: total stillness on the water. If a breeze is blowing enough to create movement in your regular decoys, you don't need motion decoys.
Motion decoys are also good in grain fields where the motion helps bring out the profile of the decoy against the background.
Finally, be careful not to shoot them. It's one thing to shoot a plastic duck decoy that costs under $10 to replace, or next to nothing to repair with rubber cement. It's quite another to shoot the battery casing out of your fancy motion decoy that cost you $150 or more.
3. Consider a "confidence decoy". These include crane, heron and gull decoys. These are not necessary by any means, but can make a difference sometimes when ducks are wary. A confidence decoy tells the ducks "things are ok here" and "it's safe to land in this spot."
4. Pay attention to your spread design and the wind direction. Ducks tend to fly into the wind. This is really handy on those cold mornings when it works out that you can position your blind so that you sit with your back to the wind and face out to the ducks flying into it. Also, ducks will often look for the calm water on a windy day.
For example, if the wind is coming from the north, set up on the north end of the water and face the south. The water directly in front of you will likely be calm for some distance out from the shoreline because the brush or topography on the north shore blocks the wind. (see diagram below)
Set your decoys in that calm water in an arrangement that leaves room for ducks to land. Place them in small groups - not as individuals evenly spaced like dots on a polka dot table cloth. Put them in groups according to species, perhaps, or based on optimal shooting for the guns in your group. Leave gaps of open water between the decoys groups so that groups of live ducks can land amidst the decoys.(see diagram below)