Good thread is thread that compliments the project you are sewing.
If you are doing a quick craft project that you do not care about, then the thread you use probably does not matter too much. If, however, you are working on a special project that you want to looks just right, the thread does matter.
This morning, I was explaining to one of my sewing machine repair customers, that her forty year old five for a dollar thread was not going to sew they way she wanted.
She responded, "I know I have sewing around the world with that thread on this machine."
Sometimes, a new spool of thread is needed. Sometimes, a quality thread is needed. Sometimes, the old, deteriorated, rotten, cheap thread should be thrown out.
So how to you choose a good thread?
First, look for quality. Look for long fiber threads. If you are using natural fiber fabrics, you may want to use natural fiber threads like cotton or silk. If you need strength, you may want polyester. If you are quilting, use machine quilting threads.
Never use hand sewing or hand quilting threads on your sewing machine. Avoid fuzzy threads like cotton covered polyester threads.
Match your threads to your project.
Finally, consider that if you use quality threads they will cause your sewing machine much less trouble. Junk threads can mess up any sewing machine.
When an average sewing machine repair today costs around one hundred dollars, an ounce of prevention can be a big investment.