through the whole pile, and once i got started, i separated out short pieces (see upper middle of picture), again to avoid digging through the whole pile. the short pieces are useful as you get to the corners, and saves you some trimming of long pieces!
i also recommend trimming to width ahead of time. my cutting mat (as you can see in the picture) was totally covered, so it was helpful to cut long strips that were too wide before getting started. all of my pieces were between an inch and 3 inches in width, although i usually kept width under 2 inches.
pick another strip long enough to stretch diagonally 