What I do for swamp hunting is find where the roost is first of all. Then, find where the birds are landing (ie eating, loafing etc), set up near that with some decoys, the amount depends on how many birds are usually on the swamp. I've put too many decoys out on a swamp and the woodies flare from them because it doesn't look natural. I've also not put enough and they don't pay any attention to them. The best piece of information I could give you is to just hunt it, go through some heart aches we all have gone through, not all ducks are the same.