After you finish packing, tap the bottom of the piece with a metal tool, it smooths everything out.

Another possibility in addition to what Sarah has described is the use of a finishing enamel layer ( e.g. Fondant Finission of Soyer ) . This is a low melting transparent flux which you would fire as the last step to even out the hills and valleys.

This last layer should not be wet packed but rather sifted.

I have been experimenting with brushes, and I have found that a #2 round works much better than the very fine brush I was using before.   Using a suggestion I found in one of the books I'v been reading, I also tip the container of wet  enamel, so that I can pick up enamel which is just above the water line for use in the wet packing.  This seems to have the right consistency. I then tap it as suggested, which also helps.  I haven't yet tried the finishing layer. 

I've been practicing my wet packing with flux on bare copper.   I know it would be better to sift this layer so as to get smooth, even coverage, but for practice it really helps me to see where my technique is still lacking -- if I have missed any spots, the oxides will show on firing.  

While I no longer have many hills and valleys, I'm surprised by how many spots have turned black with oxide after firing.  I always let the piece dry before firing, and it looks like there is full coverage when I inspect it after it has dried.   I've attached a picture of one of the pieces.  It is as if the flux has moved during firing.   

Any suggestions on what might be happening?

I'm still an enameling newbie so I hope someone else answers you as well, but if that's just flux, to me that looks like a combination of over-firing and not quite enough enamel.  I also think it looks really cool

Maybe sift the flux, then practice with a dark transparent so you can see the hills and valleys with the intensity of the color instead?

If you stir the enamel slush it happens often, that you stir little air bubbles into the slush. Also if you the slush with a watercolor brush pick it can happen, that little air bubbles come between the brush-hair. Air bubbles can so come into the enamel shift. If this air bubbles gets not removes thorough, they form after the firing pits!

Alternative to brushes or spatulas one can use tusche-pens (rendering- or caligrafie-pens) with a wooden holder. This pens are in different tip-forms available. The most participants in my enamel courses loves to work with the pens.

Success! This time I used a scoop with a little bit of extra water in the enamel that I picked up. I smoothed it with the back of the scoop. I tapped it to settle the enamel, wicked off the extra water, dried the piece and fired it. A picture is attached. Thanks everyone!

Now that looks very interesting -- I definitely can see the possibilities. Where do you buy them?

Don Viehman is one of the Cloisonne masters who taught a class I was fortunate to attend. The tip he gave us was to hold the piece between your fingers (by the edge) and gently tap the edge with your spatula or spoon. The grains settle to a nice smooth surface. You can then wick the excess moisture by gently touching the edge of the enamel.

I believe that success in wet-packing has more to do with the amount of moisture than the tool that is used. Too much moisture, and you will have trouble getting the grains to stay on your tool. Too little moisture, and you will have lumpy application. Continue to add water to the area that you are packing with a separate clean brush. The rippling or tapping will be more successful if the water content is just right. This is a question of practice. The little grains of enamel don't 'hold' moisture - they wick it, and a little more moisture will make the grains settle so that they are smooth

Tapping or rippling (drawing a ridged tool along the side of the piece) will also allow trapped air bubbles to escape

I've just started to experiment with wet packing, and I'm having difficulty with getting a smooth layer for firing -- lots of hills and valleys!    I've tried adding more water to spread it around, and while that helps the coating of enamel is still not smooth.  I've also tried using the side of my brush to smooth it over, rather than just poking or dabbing at it. However,  at the moment all I have for applying the wet enamel is a very fine brush without much surface area.  I am thinking that if I have a broader brush, then I might be able to pat it down more evenly.   

Any suggestions?  What brushes or other tools are you using for wet packing?