I find that for every grade up and down and then up and down at 90 degrees to the first direction is pretty effective. in places this isn't always possible and you have to resort to circular. You will soon be an expert - fear not. Stay dry to 600 with the paper. Works better.
I've just finished mine. It's nowhere as shinny or as good as you're case though. I blame it on the wet paper I received from eBay. It was proper shite and once wet just fell apart :-( However I'm happy enough with the final look. Removing the black paint was a real pain though..