Advice From A Technician

My number one tip for new sewists and quilters is an extra dose of patience. So many times I get a machine and I can trace the damage back to a thread jam that was hastily removed, thereby causing further damage to the bobbin case. Learning to sew should be fun but it will have it's frustrations. My recommendation is to get advice from other people that sew or consult with me if your machine is giving you problems.

One thing that people rarely think about is inspecting your bobbin for damage. Yes, the bobbin. Not the bobbin case, but the outer edges of the top and bottom of the bobbin itself can sometimes get damaged causing thread to snag or break. It may even be easier to just use a different bobbin for testing, and if the problem goes away then throw out that bobbin!

Threader malfunctions -- while most manufacturers say a size 75 needle is the smallest size needle you should use with the automatic threader it's sometimes overlooked that the weight of the thread is relative to this system working. If the thread is too thick you'll end up damaging that delicate little threader hook. If it were my mother's sewing machine I would tell her don't use the threader with anything less than a size 80 needle to be safe.

Skipped stitches -- normally this is a direct indication that the machine's settings are out of factory specifications and the machine will need professional servicing or repair. Most shops would be happy to check that machine in for repair and charge you a full service fee, but you might save yourself some time and money by following these recommendations: 

Install a fresh needle. If the thread jammed even slightly, if it barely hit a sewing foot or a zipper or pin then it could be bent just enough to not be seen by the naked eye but still bent enough to cause the tolerances to be off.

Re-thread both the upper and lower thread paths from scratch, ensuring that the upper thread is in the tension plates (you should feel resistance when pulling the thread when the presser foot is down), the check spring, the take up lever, and any necessary thread guides.

Verify you're using the right needle type and thread type for the given project (some fabrics will require specialty needles). You'd be surprised how often I see a machine come in threaded up with hand sewing thread because the customer was in a rush and frustrated so they grabbed the strongest thread they have laying around, but unfortunately using hand sewing thread on a sewing or quilting machine can cause more damage.