Threading with the presser foot down
What happens: The thread may not seat correctly in the tension system.
Try this: Follow the manual, raise the foot when instructed and rethread in the specified order.
Skipping the test scrap
What happens: The first seam becomes an expensive test on the finished project.
Try this: Test the exact fabric, layers and direction of stretch before sewing the project seam.
Pulling fabric through
What happens: Pulling can distort the seam, bend a needle or interfere with cutting.
Try this: Let the feed dogs move the fabric. Guide direction gently and keep hands clear of the blade and needles.
Ignoring needle condition
What happens: A bent, blunt or unsuitable needle can cause skipped stitches that tension changes cannot solve.
Try this: Fit the type and size specified for the machine and fabric, with the needle fully inserted in the correct orientation.
Changing every tension dial
What happens: Several simultaneous changes hide which adjustment helped and remove the route back.
Try this: Record the baseline, identify the misplaced thread and change one relevant setting by a small amount.
Forgetting differential feed
What happens: Stretching or gathering may come from fabric feeding, not thread tension.
Try this: Use the manual's starting point and test a controlled differential-feed change on matching scrap.
Treating the manual as decoration
What happens: Generic advice cannot know your machine's threading order, safety interlocks or starting settings.
Try this: Keep the exact model manual beside the machine and use it as the authority for setup and safety.
A calm correction order
Start with the manual and the last thing that changed. Record the settings, rethread correctly, check the needles and test on matching scrap. If the stitch still looks wrong, use the serger stitch-problems troubleshooting order before changing several controls.