My older sister tought me. I remember sitting on our bed with all of our shoes out and I would copy what she did. It took a few days of watching her but I got it. Maybe you can show him and let him just sit and practice. Try the different songs and different ways to tie shoes.
My grandpa used to use the ties of a bathrobe to show the concept. It's easier to get small hands around those big cushy ties. And then when he gets good at tying the BIG ties, you can move on to the small shoe laces.
I learned because I loved to read and there was this One book that was the shape of a shoe and had laces. My teacher said I could only read it if I could tie it back when I was through. Curiousity killed me and I taught myself.....it's just going to take practice.