You HAVE to make the humidity rise in the cage before the shed even starts. This can be done by sealing off most of the screen lid with duct tape, spraying the inner side of the cage as needed, and putting wet sphagnum moss (unmilled) in the cage with your snake.
If your snake still has retained shed pieces, soak him in a few inches of warm (NOT hot) water in a lidded, escape-proof rubbermaid for an hour or so. Then gently peel the skin off using the pads of your fingers. If the eyecaps remain, I'd visit the veterinarian.