First, I try to identify where the thread is breaking--at the needle or somewhere else in the thread path. I also put lines of silicone down the cone/spool to help lubricate cotton thread that appears dry or fuzzy. I have also had the nick in the spool problem mentioned above and done the same plus I use a spool cap. Using an embroidery needle with it's larger eye and sharper point may help. I have had spools that have bad sections of thread on them and had to pull yards & yards off. Some spools I have just pitched because of slubs and I even had one spool with several knots in it.