I found that I needed to tighten the upper tension when FMQing. I crank it up to 9. This really helps on the back side.
Also had to learn to either sew faster to match with my hand moving speed, or move hands slower to match the machine stitch speed. I settled with move hands slower to match machine speed.
Good luck. It will take time. I've been doing this for over 10 years & I still don't think I'm all that good at it.