I have drawn designs on quilts to FMQ. I also like to cut out a simple template, put double stick tape on it, and FMQ around it, moving the template as I go. The book Mindful Meandering by Laura Lee Fritz has a lot of continuous-line quilting designs that you can use, as well as tips for marking your designs. I bought the book from Amazon.com.
Just relax and go for it. Everyone says practice, practice, practice. I find that my stitches are always a little long when I first start stitching, and get better as I go. Even taking a break to change bobbins will interrupt my rhythm. Thank goodness there are no quilt police at my house!
Have fun.