It depends on your hunting situation, and species of your decoys. If you are using decoys such as bluebills, or redheads, place them in tight groups. For puddlers I usually keep mine 4-5 feet apart. Puddle ducks don't like flying over other ducks in order to land, so you need to create a landing zone. All this is, is an open spot for the ducks to land in. Wind conditions, and the position of your blind determine where the landing zone should be. Obviously you want the ducks to land in front of you, so create an open area in front of you. So there should be no decoys directly in front of you, except for maybe a pair close to the blind. Also, ducks land into the wind, so if posible, position your blind so the wind is at your back. Very important, I see a lot of hunters make the mistake of placing their decoys to close to land, your closest decoys should be no closer than about 10 yards from the shoreline, and your farthest decoys should be no farther than the range of your shotgun.