The method I use, I learned decades ago, can't remember where it is from but it works. Prepare a sample of the fabric/fabric sandwich, thread the machine with the thread you intend to use, one color for the bobbin and a different color for the top. Set the machine with a wide zigzag and stitch for about 2 inches. Check both sides, neither side should show stitches from the other side. Adjust tension from top. Don't mess with the bobbin tension. I have a spare bobbin case for special bobbin uses.