When I was doing it on my regular ole sewing machine, I would go from the middle out because it let the "extra" ease out to the free edges.
Now that I have a frame, I normally go from side-to-side of the quilt. On bigger ones or double stuffed, I'll still start in the middle and work my way out.
I like to quilt on the face of the quilt. That way I can kinda watch out for seams. I dunno what the "proper" way to do it is. :P