Once the color coats have thoroughly cured, it's time to start color sanding.  This was originally made popular by paint & body craftsmen that had sprayed a custom lacquer paint job on an auto body, and wanted to really bring out the deep shine.  It is also a very popular and successful method in the scale model world, particularly with model cars.  Anyhow, look closely at the painted surface: if you used enamels, most likely it has a slightly rough, "orange-peel" texture to it, and more than likely some dust particles and other imperfections in it (look closely at the photo to the left and you can see the orange-peel).  We're going to get rid of the imperfections and level the paint.  By leveling, we're making a smooth surface that allows for a great shine.  If you look at a glass surface, you won't see the rough, orange-peel texture; we're going to wet-sand the painted surface until it resembles glass in order to bring out that great shine.

Once you've leveled and smoothed the paint with the 400-grit paper, you'll notice that the shine of the paint is gone and the entire surface is a matte finish.  Don't fret; the shine will come back more than ever later!  Next, use 600-grit and do the same wet sanding of the entire exterior surface.  You'll notice that the finer grits of paper will load up with sanded material much faster, so have plenty of new and fresh sheets handy.  After you're done with the 600-grit, move to 1000-grit and continue as before.  It should take you less and less time as you progress with the finer grits, as there is less work to be done and less paint to be leveled and removed.  The key to success is patience, so don't give up now!  After 1000-grit, move to 1200-grit, 1500-grit, 2000-grit, 2500-grit, and then finish off with 3000-grit to round everything out.  By now you should have a fairly shiny surface, if you've been patient and wet sanded carefully.  Now on to polishing!

You can use a color-coordinated wax, but I prefer to use either 3M Machine Polish or Novus plastic polish (both widely available in autobody supply shops).  It helps fill and eliminate tiny scratches, and gives a great shine.  Use a soft cloth (cotton preferably), work in small areas, have patience, and when the polish dries buff it to a high shine.  This should bring forth a wonderful, deep shine, similar to expensive custom paint jobs.  The polish shouldn't have any adverse effect on decals.  If you notice any scratches or blemishes, break out the fine sandpaper and wet sand it away, working with successively finer grits until you can apply the plastic polish again.

Once you're happy with the appearance, apply your decals and re-assemble the helmet.  Congratulations, you did it!