JoeA is right, there is so much out there that is must know info on waterfowl... sate and federal regulations for your area and even down to how to cook your duck.

I'll take 2 more

1. Either hunt with an experienced caller or learn to call... never over call birds or the will become call shy and not want to come in. Sometimes calling isn't even neccessary
2.Scout, scout, scout.... get out there and find out where the birds are at and how they are working in certain areas. Talk to other hunters about what they have seen and where they may be hunting. Nothing worse than two groups of hunters cramming into 1 hole or you walking into an area some one is already hunting.