Your dog needs to learn to trust you and to go where you are telling him to go. The dog isnt going to see where every bird falls. You should work on 'blind' retrieves with the dog. The dog should be able to recognize simple hand commands like 'over' (sticking you right or left hand out) and 'back' (hand up over your head).
Once the dog knows these, you can send your dog for birds that it doesnt know where they are. A dog trusts its nose to find birds that it didnt see go down and is normally going to work into the wind. The dog needs to learn to trust your commands, so you can get him/her downwind of the fallen bird. This is VERY helpful on crips that fall on land....obviously in water, the dog will more than likely be able to see the bird.
Get him/her used to sitting still, blow duck calls around her, and of course the dog should be used to gunshots. Ive seen dogs start howling at goose calls before because they werent used to hearing them.....:bang: