If your ribbon is longer or you're using more than 12 pixels, consider zigzagging around two strands of conductive thread together for less total resistance.
On one end, stop short of the ribbon's end and leave tails about 10 inches long for sewing to FLORA.
Pick up the other tail and stitch around GND on FLORA.
Tie knots and seal with clear nail polish or fray check. As it dries, pull knots tight, then cut tails short when the adhesive is dry. For more tips, check out our Conductive Thread guide.
These thread connections are pretty close together. To help prevent the knots from knocking into each other, alternate which side of the ribbon you tie off. For example, tie knots for GND and SDA on the front side and SCL and 3.3V on the back side.
Seal all knots.
With another piece of conductive thread, stitch around the pad marked - on the pixel to secure it to the ribbon, then weave the needle under your zigzag stitch to put it in more contact with the conductive thread ground line. The more thread in contact with this line, the better the power delivery will be to the pixels.
Use a marking pen to measure where each other pixel will go-- ours are 4.5 inches apart.