Negative painting

Start with something simple. Draw some simple clouds.
Now prepare a wash of cobalt blue and a wash of Cobalt blue with a smidgen of Alizarin Crimson.
Wet your paper and quickly paint with your first wash around the clouds.
Clean your brush and add water to your edges to make them soft and smooth.

Let your painting dry and add some color effects with your second wash. Again smoothen the edges with clean water.

Try it, it's fun and you get some amazing effects!