Objective: Build muscle memory by sewing straight lines, corners, and curves on scrap fabric so your seams come out even and controlled before you make sellable items.
The difference between a hobby seam and a sellable seam is consistency, and consistency comes from guided practice rather than guesswork. On the MC6650, the etched lines on the needle plate to the right of the needle mark seam allowances (1/4", 3/8", 5/8"). You keep the raw fabric edge riding along the chosen line while watching the edge, not the needle, so the seam stays parallel. Set a straight stitch (default stitch 1) at length 2.5mm for general sewing. Use the start/stop button or foot pedal, and keep speed low using the slide speed control while practicing. To lock stitches, backstitch 3-4 stitches at the start and end by holding the reverse button. For corners, stop with the needle DOWN in the fabric (press the needle up/down button so it ends down, or use the handwheel), lift the presser foot, pivot the fabric, lower the foot, and continue. For curves, sew slowly and make tiny steering adjustments, letting the feed dogs pull the fabric rather than pushing or pulling it yourself.
Example: Take a 6"x6" scrap of woven cotton. Draw a straight line, a right-angle, and a gentle curve with a fabric pen. Thread up, select stitch 1, length 2.5. Line the fabric edge on the 5/8" guide, backstitch, then sew a straight line keeping the edge on the guide the whole way. At the drawn corner, stop with the needle down, lift the foot, rotate the fabric 90 degrees, lower the foot, and sew on. For the curve, slow the speed slider to about one-third and ease the fabric through, correcting direction every few stitches. Backstitch at the end. Inspect: your stitches should be evenly spaced and the seam should stay a steady 5/8" from the edge.
Try it: Using scrap woven cotton, sew three 5-inch rows: one straight line held on the 5/8" guide, one with a 90-degree needle-down pivot in the middle, and one following a drawn gentle curve. Backstitch at the start and end of each. Compare the three seams and circle any spot where your line drifted more than 1/8" off target.