i'll take a crack at this one.
first, you need to dry the trimmings. i separate mine into two piles, fan leaves with almost no resin, and sugar leaf with lots of resin (the stuff close to the bud).
after they are dry, i run mine through a flour strainer. i try to get rid of any stems or anything else that may puncture the screen.
after that, it is ready for the screen. i use 120 or 160 micron (i think) silk screen. you can buy a big sheet for $25 or so at a print shop. i constructed a cheap frame out of 2x2's about the size of a full length mirror, stapled the screen to it as tight as i could, and that's it.
lay a big mirror down. lay the screen frame over it (build the frame to the size of the mirror or slightly smaller).
gently rub the trimmings over the screen, about a handful or two at a time. after a few handfuls, clean off the screen and remove it. use a credit card to pile the kief on the mirror into piles and eventually jars.
i can post pics if you want. i have some trim right now that i can turn into kief.
best of luck!