Smoother gradients would be a good first step but you\'ve got the basics down.
Just to reiterate what Mosch has shown in his quick pic - if the surface is curved or angled in the right way to reflect the sky (upwards), show the sky; if it\'s curved/angled in the right way to reflect the ground (underneath), show the ground. This should help if you have trouble visualising it:
Last thing to add are tiny pinpoint highlights in pure white here and there (with a consistent point of reference) to really make it look \'shiny\'.
Einion