I would use a small sharp knife to first cut the stem end off, scrape out as much of the seed as you can, slice crosswise and then chop using a larger knife (or a mezzaluna), or as Mr V suggests, use a quick pulse or two in a blender or food processor.

I love your suggestions. I am using the dried chilies to season my roaster chicken, so the pieces are rather small. The next time I will slice them on the board, remove the seeds, and then use the bag method to gather my ingrediant and to avoid flying peppers! Thanks!

I sometimes break them up in a blender. That way they do not fly everywhere and I can get them to a point where I like them. A couple pules will break them up and bit more will turn them into powder.

How small are you trying to get the pieces? I would probably use the side of a chef's knife, and push down on the chilies to break them into smaller pieces. I bet you could also hold them inside a plastic bag and cut them into slices with kitchen shears.