2 handquilted quilts I marked in advance with a water soluble pencil and it worked very well for me. These were all marked on light fabric. I have used chaco liners to mark straight lines but I do those as I go. I also have a Fons and Porter mechanical pencil with white lead for dark fab. that brushes out fairly easy so I only mark as I go with that one too. Transdoodle transfer paper is a a chalky paper that you can transfer designs onto the quilt top. Again, this brushes out very easily. I usually end up going over it again the F&P pencil and only mark out a hoopful at a time.
I have read many here use a sliver of ivory soap with excellent results. I have yet to try that one. I have to agree with Jan though, those water soluble graphite pencils are great. And first wash I do not use soap. The instructions on my current water soluble pencil mention that some laundry detergent and even mild laundry soap may contain chemicals that can interact with the graphite and make it not come out all the way. So first wash plain cold water then I carefully inspect to make sure all marks came out before drying.