When I first started obedience training my dogs, the training instructor, who was a German immigrant, told us that when he was in Germany, his father taught him how to drive oxen.
He said that his father told him "The first thing you have to do is hit the oxen over the head with a two-by-four to get their attention".
I don't think he meant that literally, but the point was that you can't train your dog if you don't have your dog's attention.
Different trainers use different techniques to get the dog's attention.
The one I use, and recommend, is a sharp short jerk on the lead right after a command is given.
For example, the very first command I give a dog just starting obedience training is "Heel", giving a sharp jerk on the lead for attention, then getting the doginto the heeling position.
As soon as the dog is in the proper position, the dog gets lavish praise.
The strength of the jerk is a function of the size of the dog.
It should be just enough to get the dog's attention, which, in the case of a large dog like an adult Newfoundland, would be quite strong.
The use of a training collar helps.
This can be either a slip collar, sometimes called a choke collar, or a pinch or prong collar.
A martingale collar also works.
The proper location of the collar is high on the dog's head just behind his ears.
The slip collar (choke collar) has to be put on the dog correctly to be effective.
With the dog on the handler's left, the part of the collar connected to the ring to which the lead is attached, goes over the dog's neck.
Put on this way, when the lead is tightened, then loosened, the collar becomes loose around the dog's neck.
If the collar is not put on correctly, when the lead is tightened then loosened, the collar stays snug around the dog's neck.
The pinch collar (prong collar) should be fitted so that with the lead loose, you should be able to get just the tip of you little finger between the collar and the dog's neck.
The most common training error I see is where the trainer (owner or handler) pulls on the leash instead of jerking it.
This not only doesn't get the dog's attention, but it let the dog thing he's in the game of tug-of-war, which he wants to win, so he pulls back.
The technique I've found most successful is to give a sharp jerk immediately after the command, then soft little jerks coaxing the dog into position with verbal encouragement.
And give lots of praise when the dog responds to the command correctly.
Treats can also be given along with the praise.