You polish the blank by putting finer and finer scratches on it, till
you can't see the individual scratches. The smaller the scratch,
the higher the gloss. So you want to make sure you're not
accidentally putting bigger scratches in there. Never put your
sandpaper on a dirty blank.. it already has particles of the last
grit on it, and you'll grind those into your finish.
i think you're getting the idea that wet sanding is a good idea.
But another important point is not only to sand wet, but to
WASH your sandpaper and the blank.
I you're humming along at 1000 grit and there's still a few
particles of 400 somewhere on the blank (or on the sandpaper)
you'll put some nice scratches on the blank.
I use the micromesh, and I keep them in a little tupperware container
of water with a bit of dish soap. But I also rinse them in clean water
(not the tupperware .. that has EVERY size particle floating in it!)
before I use it on the blank. A bit of wet towel to wipe down the
blank helps, too.
Someone mentioned good sandpaper, and that's important. Cheaper
papers don't have a consistent grit size, so you might THINK you're
sanding at 400, but some of the particles are 200 or 100 .. so you're
killing the finish. Your work is too imporant use cheap sandpaper.