We have tried multiple watercolor resist techniques in the past, but have greatly enjoyed a new art technique: watercolor wax resist. You need paint brushes, watercolors, water, watercolor paper and a white candle.
Draw on a sheet of paper with a candle, then paint with watercolors. You will see that the place where you drew with the candle remained blank. Allow the painting to dry completely, then repeat the process ( draw with the candle first, then paint.) You can repeat this process as many times as you wish.