This exercise will seem daunting because of the subject matter I have chosen to use but don’t let that scare you off. You really could make a wonderful painting with a subject like a boat, a house, or an arrangement of flowers. The beauty comes from the quality of the shape you draw highlighted by the use of white paint.
Take out several pieces of watercolor paper and tone them with an interesting light middle value wash, try not to have too much going on or it will be too confusing. To start probably a wash or Raw Sienna or Burnt Umber would be great. Then draw a couple of shapes, really trying to get a good silhouette, because this is where the white paint will be creating a wonderful negative shape. Apply the white paint, I use Titanium White DaVinci Brand, in several coats and get an irregular finish, use less water than you are comfortable with. If you need to add some detail colors to your centers of interest but use them sparingly. You want the drawing to really show.
Give several of these a try and you should find it not only fun but also very expressive 15 x 22 watercolor paper toned with cadmium scarlet and raw sienna
15 x 22 watercolor toned raw sienna and halloween orange, American Journey Color
22 x 30 watercolor toned with Raw Sienna