What’s the most common training mistake people make with a new puppy?

This one’s easy:  Not starting training right away. It’s as easy as saying good sit when the puppy sits anyway. Say, good potty when potty comes out in the right place. Say good puppy when the puppy chews on a toy.

Catch the pup doing things right from the very beginning. This makes the pup want to do more good things and it teaches word association – what is this sit thing I just did? Oh, that is sit – they like that – let me try it again.

Training also means lots of social time – other people, other dogs, uncommon noises — so your pup is confident in different situations.  Also, let the pup explore – don’t be the protector all the time.   Some things are worth learning on their own.   (Chewing electrical cords are not!)