There is no right or wrong. "Give them a place to land" "make a J" etc are ok suggestions, but I've had plenty land right in the middle of the spread. That said, I usually leave a pretty big empty space right in front of me; this gives big groups a place to land, and keeps prying eyes off of me. I've never seen ducks organize to form specific shapes in the wild...
My general approach: if I'm hunting an area with a lot of pressure ie I'm going to have someone within a few hundred yards calling the same ducks I'm calling, a bigger spread is better. If I'm in an area where there are a lot of high flyers, migrators, or just really large groups of birds in general, a bigger spread is better. Keep in mind though if you've only got one person calling and 100 decoys, you aren't going to sound natural at all.
What I really prefer though is to find honey holes...places birds really want to be, far away from anyone else. Within two hours of Eugene I've got a number of public places I hunt on a rotating basis that I'll give the honey hole tag to. I've lived in Eugene for 2 years now, couldn't hunt last year though because I was working 7 days a week, so it's not like I've been scouting this area for a decade. Put in some time scouting and you won't need 100 decoy spreads. I've hunted quite a few places where I start the morning off with zero decoys. Yes, zero. They're small holes the ducks just want to be. Or for the holes that are big enough that they *could* land out of range, a single pair of mallards. For the most part I sit quiet, throw in a soft quack and some drake, and the birds sit right in my lap because I'm where they want to be. If the birds are coming to you, why give them any reason not to? (bad calling, shiny, not-moving plastic duck replicas...) If there are any groups flying high that look like they're on a mission to somewhere else, call like normal and toss out a few keel weighted decoys right then. This "technique" only works in rare instances where you are right where the birds want to be and there isn't any other water nearby, but it's by far the best
Nobody cares about your season totals. Especially if you pay to hunt private.