My method is a bit different than Ninja's, but I don't use anything wet.
As I harvest, all the popcorn bud goes into a special bowl. No trimming, I just pluck 'em off and throw them in there. Fan leaves, branches and anything I trim by hand goes on the floor or in the trash bucket next to me. All the nugs either get trimmed by hand or go into the SpinPro, then into a finished bucket to be placed on drynet. But I digress lol
The reason I explained all that was to give you an idea of my source material. All little popcorn bud really. I save it up in a big pan and let it get bone dry.
When I'm ready I get 10-15 lbs of dry ice pellets. Only place I ever got mine was Elm Ice and Oil in Falmouth. I don't believe Walmart in Maine has it; I could be wrong.
I have this little plastic bucket that my 220 micron bubble bag fits over nicely. I crumble up enough bud to fill the bucket about 1/3 full and throw in some pellets..it doesn't take too many really. 10 at the most. Put the bag over the bucket and pull it down around the bucket, so the mesh forms a cover for the bucket. Shake vigorously for 20-30 seconds..AT THE MOST!
Have a nice clean surface like a tabletop to work over. Invert the bucket and shake some more, like a salt shaker. You can also occasionally shake laterally to mix it up and sorta sift. Keep a close eye on what's coming out. It will likely be quite blonde in color at first. You will notice it start to get a green tint to it. This is leaf material that is also being broken down small enough to fit through the mesh. At this point, the longer you shake the more contaminated the end product. When to stop is up to you, and learned from experience.
The resulting kief can be heated, pressed, kneaded, used in edibles, whatever. The yield is phenomenal at least with what I use.
See also my thread on a neat press I made:
https://www.rollitup.org/maine-patients/530284-my-new-jack-puck.html