The preparations are the same as when working with Hexagons or other paper shapes:
Place the paper shape on the wrong side of the fabric (pin the paper in place if needed). Cut the fabric patch at least ¼ inch (6–7 mm) larger than the paper using good scissors. It is important to have enough fabric excess to easily cover the paper shape all the way around—this is your seam allowance. Don’t make your life more difficult than necessary!
Fold over the seam allowance along the edge of the paper. Starting in the middle of the edge, stitch through all the layers with big basting stitches (¼ inch or bigger) along the folded edge.
At the blunt corner of the diamond, fold over the next fabric edge (hold in place) and stitch over the fold to hold it down—no backstitching needed.
Continue the baste along the edge, but stop ½ inch (≈1 cm) before the tip of the diamond. It is not necessary to tuck under the excess fabric “tail” at the tips—let your tails wag! Simply fold the next edge over and secure with a basting stitch.
Continue to baste around the diamond as before. When you reach the other tip, tuck the last seam-allowance edge under the tail flap. The new edge always folds over the already basted old edge. This way the tails point in opposite directions and will nestle into neat rosettes on the back of the quilt when the diamonds are sewn together (just fold them out of the way while sewing).
Finish off with an extra basting stitch in the same direction. Alternatively, weave a few tiny basting stitches through the seam allowance (as shown above) and snip off the thread.
DONE!
To sew two diamonds together (use your pattern for reference), place the shapes right sides together and overcast with small whip stitches, catching just the very edges of both pieces. About 6–10 stitches per inch (one stitch every ~2 mm) is ideal.
At the end of the seam, add another diamond and continue sewing, or—to finish—make 2–3 backstitches and secure the end of the thread by weaving a few tiny stitches through the seam allowance. Then snip off the thread.
Once patches have been added all around a paper shape, the basting stitches can be removed. Simply snip the basting thread in two places, grab the ends, and pull them out. Remove the paper by gently pinching in the middle and easing it out. The papers may look a little worn, but—unless torn—they can be smoothed and reused.