I hope you keep at it. Mine was consistenly terrible until it magically wasn't anymore. There wasn't even any transition from terrible to good. It just happened. Lots of good tips here but don't always assume loops are automatically a tension/threading issue. They are often because you are moving the fabric too fast with your hands. For me this seems to be the magic formula:
80/20 or better batting. All poly is always problematic for me
Leave feed dogs up
Turn tension way up