I know this is perfectly normal puppy behaviour but Zehat's the best way to teach him otherwise? I offer another toy to bite/ pull on. Is it a matter of keep doing the same thing until he gets the message or grows outbof it?
I'd teach him a "leave" or "drop" or "that's enough" cue, by encouraging him to play tuggie with an appropriate toy (be wary of tugging too energetically until his adult teeth are through) and then practising him letting go on cue.
A clicker helps, but you can do without. Get him playing, then make the toy go "dead" by stopping it moving. He'll probably let go, but if not you can use a treat to lure him off it. When he's reliably dropping it when it goes dead, you can introduce a "drop" cue. Give a treat when he drops it, then introduce a "get it" cue and recommence the game. You won't need a treat every time; once he's got the idea, the recommencement of the game becomes the reward for dropping on cue.
He'll probably still grab at inappropriate things for a little while but it's not too much of a hassle if you know he'll let go when told, and he'll soon learn that the only thing he's allowed to tug on is his toy when YOU invite him to.
Some people don't approve of playing tuggie - and particularly don't approve of ever letting the dog "win" - but my dog (and other tug-obsessed dogs I know) NEVER grabs stuff other than a toy, and then never grabs the toy until told to "get it".