@CountLoliDee watercolour reveals alllll sins! probably the only way to avoid it completely is lightboxing or similar. To minimise show-through I sometimes roll a kneaded eraser over the whole thing until I'm left w/the ghostliest lines I can still see, but I think an equally effective way forward is to accept those marks & make them part of your plan. Letting them submerge within your colours–e.g Sargent–or even leaning into it by using colour pencils can look great–e.g http://jamesgurney.com/site/images/pencil-and-watercolor