Setting Bobbin Tension
This video shows how to set bobbin tension on an L sized bobbin. Watch out for the cardboard on your cardboard bobbin brands, some of them will rub the edges of your bobbin case and seriously mess with your tension adjustment and actual sew. Tear the cardboard out if you cannot get the bobbin case and bobbin brand to coexist, but ideally it would spin without ever brushing the side of the case.
Some techs like the bobbin a little tighter than shown on this video, so a little extra small turn is fine in that case.
If there is an extra removable spring inside of the bobbin case, remove it if you are using cardboard bobbins; it adds unpredictable tension with cardboard.