A good duck decoy spread can make the difference between a successful hunt and a busted hunt. By keeping a few basic principles in mind, hunters can navigate most hunting situations.
1. Pay attention to the wind direction. Ducks fly wherever they want to, of course. But they often fly into the wind.
2. Notice what the wind is doing to your water. In stiff winds, duck will often look for the calm water. If you are hunting with your back to the wind, the calm water might be right in front of your blind - exactly in the ideal landing zone. Don't stuff this area full of decoys.
3. Designate a landing zone that is well within shotgun range - 25 to 45 yards is ideal. This close distance gives a high percentage shot for a quick kill and a successful retrieve if the duck sails off.
4. Keep your landing zone mostly clear. Sometimes, 1 or 2 decoys in the landing zone will help draw birds, but generally keep it clear.
Below are some diagrams that lay out a basic duck decoy spread. These will give you some ideas for how to hunt your particular situation.
The Mixed "C" Spread
I call this the Mixed C spread because the decoys are mixed birds - pintails, mallards, teal, widgeon, etc. - and they are placed in a general C pattern around the edge of the shoreline with the blind in the middle. This places the landing zone directly in front of the blind. This spread works especially well on a day when the wind is variable and you can hunt with your back to the wind. The calm water will be all along the shoreline. This spread makes for a nice, close shot of about 25-40 yards.
The Wedge Spread
This duck decoy spread is called a Wedge spread because the decoys are placed in a wedge pattern with the idea that the ducks will land in the areas outside the wedge. The wedge is placed so that the wedge sort of "points" the ducks into the landing zone. This works well when your blind is facing into the wind and the calm water is on an opposite bank. You want to fill the calm water with your decoys and "wedge" the landing ducks out into the open water closer to you. Your shots will be in the 30-yard range or so, which is perfect.
Split Groups w/Coot & Bluebill
This duck decoy spread splits up the decoys into 2 species groups, which is sometimes attractive to ducks. It shows mallards on one side of the landing area and coots and/or bluebills on the other. You can use many species - widgeon, teal, pintails, whatever. Coots, however, are a confidence decoy for many ducks. Skittish ducks will feel safe if they see coots. So, it's nice to pair your mallards, pintails or widgeon decoys with a group of coots (or bluebills if you don't have coots) to make this nice split.