I have a small sketch book that I just doodle in with a fine point sharpie marker. It's amazing how quickly your skills will improve and the benefit of just doodling is that you will develop the ability to move around a quilt without marking. What I do is start with a motif (like a feather) and then try to work my way all over the page doing traditional quilting fills, like pebbles, paisleys, spikey things, anything I can think of that will help fill in and will also be fairly even in terms of density while at the same time using patterns that are of different scales, so some large things, some small and some medium. Another thing to look at would be some of the Zentangle books-- a lot of their patterns are identical to traditional quilting patterns, and the books give very clear directions on how to draw some of them as continuous line drawings--exactly what you would want with a quilting pattern.
Rob