Objective: Learn the common sewing-industry standards for seams, stitching, and finishing so your home-business items look professionally made rather than homemade.
Hobby sewing lets you improvise; selling to customers means meeting shared conventions buyers unconsciously expect. The most important is seam allowance: garments are typically sewn at 5/8 inch (1.5 cm), while bags, home decor, and quilting often use 1/4 inch or 1/2 inch. Pick one standard per item type and keep it identical across every seam so pieces fit together. Stitch length matters too: a general-purpose straight stitch of 2.5 mm is the industry default for medium woven fabric; drop to 2.0 mm for fine fabric and raise to 3.0-4.0 mm for topstitching or basting. Topstitching is usually sewn a consistent distance from the edge (commonly 1/8 or 1/4 inch) using the edge of the presser foot or a guide. Raw edges must be finished so the item does not fray after washing: in ready-to-wear this is done with an overlock, but on the MC6650 you replicate it with an overcast stitch and overcast foot, a three-step zigzag, or a French/flat-felled seam. Backstitch (or the MC6650's lock stitch) at the start and end of every seam for durability. Press every seam before crossing it with another; pressing, not sewing, is what separates professional results from amateur ones. Finally, standards include consistency: even stitch tension, matched thread color and weight, trimmed threads, and clean interior finishes, because customers inspect the inside of handmade goods.
Example: You are making a zip pouch to sell. You choose a 1/2 inch seam allowance and set it for every seam. You sew the body seams at 2.5 mm stitch length, locking the stitch at both ends. You finish the raw edges with the MC6650 overcast stitch and overcast foot so they won't fray. You then topstitch along the zipper a consistent 1/8 inch from the edge at 3.0 mm length for a crisp line, pressing each seam flat before the next step. The result has even stitches, no fraying inside, and no dangling threads: a sellable, professional-looking pouch.
Try it: Take two scraps of medium woven cotton. Sew them together with a deliberate 1/2 inch seam allowance at 2.5 mm stitch length, locking both ends. Finish the raw edges with an overcast or three-step zigzag stitch. Press the seam. Then topstitch a parallel line 1/8 inch from the seam at 3.0 mm length using the presser foot edge as a guide. Inspect both sides for even tension and trim all thread tails.