I got a Janome 6600 in February and thought it would solve all my FMQ issues - skipped stitches, breaking threads, nests on back ... well ... until I've finally been patient enough to deal with one variable at a time those problems went with me from my old Brother to my new Janome. So ... after much frustration and much ripping I finally have some things narrowed down. I'm not trying to recreate LA quilting - I don't think that's possible. My stitching may be a bit primitive, but I'm okay with that. I'm certainly no expert, but I have moved a little farther down the path.
What I've learned:
Read everything you can because some of it will make sense - both on here and in books/magazines.
Try stabalizing the quilt with some zigzag or scallop stitches that divide the quilt into sections. Then FMQ within each section. I spray baste and this has worked very well. Also allows me to start quilting in the outer blocks without concern that the whole thing will shift as I sew.
Develop a repertoire of simple stitches. Use them until you're tired of them and then work on a few more. I started with the simple meander, added loop-de-loops, hearts, flowers, leaves (I think these are really feathers, but they feel like leaves to me), and echo quilting.
If thread is breaking it could be - tension too tight - change it a TINY bit looser, could also be dust bunnies in bobbin case
If skipping stitches try a larger size needle - I'm currently using a 16/100. After you've done that if still skipping stop and rethread both top and bottom.
When things are working take a picture of your machine to save the settings.
If stitches are not right on back - little loops of threads - tension is too loose. Tighten it a TINY bit. If big loops on back then tighten two tiny bits. Also slow down your hand movements.
Clean out dust bunnies from bobbin case with every bobbin change. Change needles with every quilt.
Be sure the weight of the quilt is supported - I put a stool next to my chair, but know people like to use small tables and ironing boards for this. I sew on my dining table with the machine far to the right - that leaves room on the left for some of the quilt.
I was making too many changes to too many degrees and creating problems as I solved other ones. So tiny changes, then sew to test the change.
Check the back OFTEN so you don't end up ripping miles of stitches.
I have made many FMQ quilts, but with varying success. I understand the idea of making practice sandwiches, but ... so far... haven't done that. Trying to finish my last project I got so frustrated I pulled out my little old Brother to finish. Hopefully writing down these hints will help ME remember what I'm doing that's almost working. And hopefully ya'll can add some others or refine mine.
What can you add to this list? (Edited to add: I have no idea why my sewing machine is upside down - interesting - or why the pic of the block is fuzzy, but hopefully you can still see what I'm talking about.)