Have you hugged your machine today?
Give it a little TLC, dust it off, dust it out and give it one drop of machine oil. It only takes 2 minutes and your machine will love you for it.
Problems? Try T-N-T
-Thread - rethread and check the thread path for stray threads left behind. Make sure your thread is of good quality and lint free.
-Needle - check the needle for burrs and bends. Replace the needle with every project or with every 2 bobbins. Needles do the tough work of punching holes for the thread to pass through, use the right one for the job.
-Tension - what your mother told you, "don't touch that tension dial", doesn't apply anymore. If you use different weight threads on the top than in the bobbin case, you need to adjust the tension. Refer to your machine manual or make a test swatch of the fabrics and threads you will be using, start at the normal setting, sew a inch and adjust until you get the proper tension.