I got 4 sanding sponges from Halfords, super fine and ultra fine (think one is 180 and the other 220 or something like that) They are about 5mm thick and cost around 4 euro a pair.
Did each wheel individually. Firstly just a good clean down with any suitable cleaning product or just water. Then used the super fine sponge to continuously sand the entire dish of the wheel. You'll want a bucket of water or something to hand to rinse the sponge/wheel from time to time. Once your happy all the marks/blemishes are gone move onto the ultra fine sponge and repeat the process until you have perfectly clean, even surface.
Again, make sure the entire dish is spotless, then its just a matter of polishing the shit outta them with autosol, the longer you spend polishing the better the shine.
So basically all you need is 2x superfine sanding sponges, 2x ultrafine sanding sponge, bucket of water, autosol, time and patience