Cleanliness is important when processing PCBs. However, for DIY use, no need to panic. Just clean off the photo resist on the board (you did resist cleaning it off after etching right?) with a little acetone, or gently scrub it off with some steel wool. Careful to get the really fine grade stuff, so as not to make deep scratches in the soft copper surface. You should be able to get the copper to be quite shiny and oxide free.

Clean off any residue in hot water.

You can make a really shiny, polished surface using 'Brasso' copper/brass polish (available in pretty much any household shop in the UK) just place a little onto a cloth, buff the board gently with circular motions, then buff off with another clean cloth and finally rinse in hot water. You don't want any residue contaminating the board!

This will result in almost a mirror finish, however you will clearly see the fiber weave of the PCB substrate material as a pattern in the shininess of the copper. It won't get any better than that. (no I couldn't get my camera to take a shot of that!) As soon a you have a shiny, residue free (don't worry about drying it, just shake off any water) PCB, progress straight to the final plating stage without delay!