Once the birds have been shot at, they will be very cautious to deek, especially mallards. The bigger the flock the more eyes they have to spot you. I'll take 2 and 3 birds all day long over a flock. So a GOOD blind is just as important or more so then the way a few deeks are spread out.
If you intend to hunt the morning, in the evening drive by some of the spots your interested in hunting, especially if your hunting fields and see if they hold birds. This has help us a LOT.
As already mentioned, keep the wind at your back and have a landing area for the birds.
Good Luck