We all know that you never need to strike your dog or puppy to teach him, not ever in his life. We know that, just like kids, getting his attention with a happy tone and big smile will be all it takes. A little reward, whether a tiny treat or just loving him up with squeally praises, presses home the lesson and makes him happy to return to work sessions again later. Naturally, the younger the puppy is when he starts this session the better. Hopefully he is 6 weeks old or so, before he has had access to something he should not have, and blissfully ruined it.
But so many things entice a puppy to chew, since it is a natural behavior for him anyway, how do you teach him what NOT to chew before something valuable has been ruined and his feelings have been hurt with scolding? The method I use is so easy and fast you won't believe you didnt think of it!
Instead of teaching him one thing at a time, which works best with behavior training in general so as not to confuse him with too much information at a time, do it all at once! Place everything you can think of on the floor within his reach. Shoes, socks, clean and dirty (two different things to a pup), 5 or 6 different "legal" puppy chewies, pencils and pens, newspapers and magazines, articles of clothing, wires, keys, anything you can think of that could some day wind up on the floor. Leave lots of space around each item so that he will have them separate in his mind.
First, take him out to go potty, we want no distractions here. Place him on the floor in the middle of all this wonderful stuff, and get on your knees or haunches to stay very close to him as he explores each item. Be a part of this "play" time with him. As he approaches each item, give him one second to sniff it so that you know he has smelled it and placed it in his brain. If it is a good item like a puppy chewie, make a happy face and say "Good chew! GOOD puppy!" [use his name] If it is a sock or other "illegal" item, make a scowl and slam your palm on the floor beside the item and say "NO chew! NO chew!" and swap the bad item with a legal chewie as you say it, wiggling it to make it more enticing to him to play with and chew, and as he goes for it say, with a big smile, "GOOD chew! GOOD [puppy]!" After ten minutes, he will be only going for legal chewies and having the time of his life. If you do this one more day with some different items, this will reinforce that only certain items are legal and some new items may turn up that are not legal because they are not the legal items. See? It works like a charm and they never forget it.
Your happy face is what a puppy wants to see more than anything. Learning the difference between what is legal and what is illegal to chew is the fastest and easiest thing your puppy will ever learn when you use this method, and it will save you and him much heartache and disappointment in the life of his training.