A good first project is a small 4 patch quilt. It's simple and quick and provides an early success. If you're worried about him pricking his fingers on a pin and getting discouraged, use elmers washable school glue sticks instead of pins.
I don't hand sew at all, so the kids learn machine sewing and machine sewing etiquette. The most important etiquette is to respect the needle as it goes up and down. We use the glue method to line up edges, and that seems very natural to them. So far, they've done a pretty nice job of sewing, and seem to enjoy.
The youngest I've started teaching a child is 6 and his first project was a 4 patch 'butt warmer' for his bird. He wanted to know if I cared that he gave it to his bird...I laughed and told him, no, it was his quilt and he could do what he wanted with it. I don't think the bird has ever seen the 'butt warmer', though.
For you, the most important thing is to be patient and alert. My Mom, bless her soul, used the 'here, let me do that method' to teach me sewing and that made me dislike sewing for a very long time. In her defense, she had 7 kids vying for her attention, so her need to get done quickly was somewhat urgent. We were no angels so there was always a crisis to resolve, if you know what I mean.