You learn a little everytime you go. Learning to read the birds is a big one and you will get better with each outing. The biggest thing I learned in all my years of waterfowling was...to hunt with experienced hunters. Years ago when we really got in to it, we read every book, watched every video, asked questions on web sites....but on my first few hunts hunts with an experienced hunter, I learned more than all the others put together.
Now that I'm a seasoned waterfowler, I love to take new guys. There is nothing better than seeing a kid or even an adult, take their first goose or duck. Sometimes guys don't understand why I don't pick up my gun when I'm telling everyone to take 'em. Making the actual kill shot is not important, it's the set up, reading the birds, the calling, and the experience to be able to wait until they are truly in your face before you call the shot. That's waterfowlingin it's purest form!