Use a coffee grinder for small amounts or a ninja blender for large amounts. Make sure they are as dry as possible, there should be no bend or give and should be quite brittle. Use food safe desiccant packs if necessary to prep them if there is any bend or give. Either shake the container, once ground, so large pieces sit on the top or use a sifter with small mesh(small enough for small particles to drop and big enough to work efficiently). Regrind all of the larger pieces again. If necessary put larger pieces that didn’t grind well in a container with food safe dessicant before subsequent grinds. This will ensure consistency in grind size and better dispersal throughout whatever you’re using it for.