Is your thread breaking?

If you are seeing thread breaks, how old is your thread? Is it an old spool you inherited, or picked up from a yard sale, or found a great deal in the discount bin at a craft/discount store? 

Older thread and some more inexpensive threads can be prone to breakage.
Also, is the type of thread matching the fabric you are sewing? 

Ask a quilter, what thread to use, they will tell you to only use a 100% long staple Egyptian cotton  thread, like Aurifil when sewing or quilting with cotton.  I'm not a quilter, but that makes since to use a high quality cotton thread when quilting. You want a low lint, long stable cotton thread, that is not stronger than the fabric you are sewing with. I use a comparable long staple Egyptian, that is a bit more affordable for testing tension on my machines, with two layers of starched cotton, or two layers of quilting cotton.

Depending on what I am sewing, I use different types of threads. I use a cotton or cotton/poly thread on cotton sewing projects, I use either cotton/poly or 100% polyester threads on knits. Always do a test stitch on some scrap material, to test and adjust the tension before sewing on your project fabric.

I tried using some serger thread on some cotton fabric, because it matched the color of the fabric - oops, a not  good call. My test stitch had skipped stitches all over the place! (my serger thread was also very linty).