This topic comes up a lot, and many people have differing ways of setting up for individual sewing jobs. One thing that is common to all machines and straight stitching jobs, is even pressure at the material.
Points to remember;
Match the needle thread tension to suit the bobbin thread tension. Don’t touch the bobbin thread adjuster unless you know what your doing and as a last resort.
Make certain the thread is routed correctly.
When using a new thread for the first time, start setting up with smaller stitch lengths. Then progress and adjust for longer length stitches. This makes tuning a lot easier.
Check that your thread suits the machine. Threads have different twists.
The machine I have used for the example is a repair. I have used a white thread for the bobbin and brown for needle, this is just to help me and you see that the thread is tensioned correctly.
This has been just a brief set of instructions and examples. I hope it may help some one. The Singer K196 is a repair and set up.