Been sewing for years and I still have a brain fart when it comes to tension issues. Now I remember with this neumonic which applies to the needle tension. Thread lies in top.tension to tight Thread lies on lower.
Sewing Machine Tips for Presser Feet: Adjusting the tension knob according to your fabric. Heavy fabric: less tension. Lighter fabrics: More tension. Then the presser foot will hold the fabric securely to the feed dogs & keep it from sliding.