the tension on the left side front- set it all the way at the top (like unscrewing it)
make sure your top and bobbin thread are the same, my Juki likes them the same. Every time I change the bobbin I have a practice sandwich handy to be sure nothing has changed- that way the quilt doesn't get rats nests.
I've never really had any issues with the machine so I probably wouldn't be good for help. :( I just smile at it alot and tell everyone how much I love it so it behaves for me.