How do I prevent thread breakage on my Singer 1120?

For upper thread breakage, ensure proper threading, adjust tension (which may be too tight), use good quality thread, and check that the needle is not bent or burred. For lower thread breakage, re-wind the bobbin correctly, re-insert it properly, clean out lint from the bobbin case, and adjust bobbin tension if needed. (Page 1 — Troubleshooting)