Beyond mistakes due to a total lack of experience, there are some notable ones that come to my mind. The most significant to me were AFTER I 'finished' my first dog. He would handle like a champ and could handle multiple marks with the best of the, AT THE TRAINING POND.
Opening day in the blind...
1) Dog port and door were COMPLETELY covered by brush. Dog couldn't see to mark and wasn't accustomed to exiting down a ramp and through brush in order to get to open water for retrieve. All of the super training references and advice I had never mentioned hunting conditions, not once.
2) Did anyone else know that ducks dive? That is one my first dog had to figure out on his own. Fortunately for him, but not for me, he had plenty of cripples to teach him this his first year.
3) Remote sit is one thing, but remote sit, stay, be steady, and wait for me to shoot something was not in our bag of tricks on opening day.
4) Marking from elevated positions (table or platform). I had to teach this mid-season in order to compensate for #1.
5) Teaching the dog to mark by sound as well as sight. Again driven by #1
I think you get the drift. At the conclusion of my first season with my dog I was almost angry because I had COMPLETELY neglected training my dog in conditions very similar to what we would be hunting. To this day, I've not found this point emphasised by the 'high brow' and 'super technical' training material that I have seen. Now, during training, my dog is seldom sent on a retrieve from the heel position. I'm more apt to have him sit on a table up on my deck, or mark from a laying down position in his field blind.
"I'll start spending less time with my dog and more with my wife when she starts fetching ducks for me"