slowblade

Hello, I cant seem to find an answer to this on the internet, so I am asking the experienced modellers how to do as the title says Ive sprayed my model with a basecoat of Humbrol 21 gloss black spray paint and sprayed over Tamiya AS-12. The surface has a few blotches and not particularily smooth but I dont want to try sand it down swith smooth sandpaper i.e 3000 grit tamiya sponges unless I scratch it. Is there any specific method to sanding and then polishing the metal to a nice finish? Do I need higher grit sandpaper or polishing compounds? Bare in mind I dont have an airbrush. Thanks, James :)