I don't have a Janome and frankly I am not that great at free motion but the main thing that has helped me is this:
Just make up a bunch of 12 inch quilt sandwiches and practice on those. What I did was used some old muslin and batting scraps. To begin I drew a stipple pattern and followed that. Then I drew other patterns and followed over and over. This will also help you to figure out what you need to do for your tension and such.
I would definitely check my needles and thread as well. My Bernina is sometimes finicky with the thread. Thread that I piece with sometimes does not work as well with the FMQ. I'm not sure why but check that out as well. Also, don't forget to give your machine a good cleaning as well. Sometimes lint and dust can cause problems as well.
Good luck and don't give up! Before you know it you'll be over this hurdle. :)