I cut two widths (1 & 3/4 inch and 1 inch) of fabric from the leftovers I trimmed off the original shirt. Then I layered the wider one underneath the narrower strip and fed them through my sewing machine.
And it was like magic, seriously. Perfectly spaced ruffles came out the other side! So much easier than basting, pulling threads, having those threads snap, sewing it again, and then spreading to out evenly.