I've used clear transparency sheets to draw my designs on, then lay the sheet over my top to see if I like it.
I've posted in the past about a class I took that teaches you how to see quilting designs every day in your life, how to utilize those designs in a quilt, and how to draw it out to see if it would work on your quilt. The class is called Quilt Whisperer 101, taught by Carla Barrett. She does beautiful work. Here's an example - you can see how she designed the quilting for one quilt, and then how the quilt actually turned out here:
http://featheredfibers.wordpress.com...esley-maisano/