how will you instruct a 3 year old boy to tie his shoe laces?

You need not instruct directly how to do shoe lacing, instead you can play with him like tying, buttoning, zippering, try to have some materials that have laces, or and after that he is use with the tying now you can introduce to him how to tie shoes, at first instruct him one by one, then let the child to it, then constant practice makes him perfect in tying his shoe laces