Take him to puppy classes, get him out and socialize him.
Let him drag his leash if he throws a tantrum, just keep it on him in the house with supervision of course, and let him drag it.
DO NOT BABY HIM no matter how cute he is!
he is a Working Thinking PRoblem solving breed and with that you will have many challenges.
He also is smart and if he can get his way, he will.
You must go to a good trainer and have them TRain YOU to train this pup.
Make sure the trainer is well versed on the breed and in good standing.
Also make sure that you read the Breed standard,
This breed is natural life saving.
wich means, if a person was drowning a newf instinct is to save them, instinct has them grab an appendage to haul them to shore if the person cannot hang on to tail or hips.
The puppy will naturally mouth you,
one way i correct this with my pups is to ball my hand in a fist, place it to the back of the mouth, this is only if he was mouthing my hand, i will immediatly do the balling of fist placing to back of mouth, and supporting back of head with other hand, it is not pleasant, and, than offer hand to him, if he licks, praise him.
if he mouths, place fist to back of mouth again.
how old was your pup when you got him?
if he did not go thru the whole bite inhibition stage, wich lasts till approx 8 1/2 weeks. than you are in for more of a challenge than if you got aan older pup