I first make a practice sandwich of the same materials I will use on my quilt. I load top and bobbin thread and stitch a little... then look at the back.
I'm purposely showing a bad start for learning purposes. I often ( as in this example) am using a 40 wt thread on top. With 40 wt thread, I'm always setting upper tension below the mid point on the upper tension dial. Mid point would usually pull the lightweight monofilament up above the top surface.., so the game is seeing where to set it below mid point.
In this first example... I set it at zero.. the lowest upper tension which you will see is TOO low.
Then look! This looks BADDDDD!
I then step up to 1 and repeat the sew and look process.
Closer but not quite!
Let's try 2!
This is a game replayed whenever a new thread manufacturer or top thread weight is loaded. This would also apply if you DO change bobbin thread. Remember,practice sandwiches are your friend!!!!!