Lay a large sheet of tracing paper over the quilt top and lightly trace block/shapes. Remove the paper from the quilt and sketch out quilting options, laying it on the quilt top occasionally to “audition” options. Trace over the final design with a fine tip marker to have it for reference while quilting.
Another option is using a thin plastic sheet. Instead of sketching with a pencil, use a dry-erase marker. If you want to keep this design for future reference, you can trace over it with a permanent marker. Or you can simply erase the design when you are done and use the plastic sheet again on your next project.