•When painting with water, move from lighter areas to darker areas. The brush will carry the darker colors into the light areas if you do not do this.

•  Don't add pencil to wet areas; it creates a darker colour that won't change.

• Shade lightly and evenly, deep marks may remain or groove the paper in places where you don't want them.

•Test unexpected color combinations on a side sheet of watercolor paper or a multi media sketchbook. Try mixing complementary colors like orange and blue or yellow and violet. See whether mixing two dark colors like Indigo and Dark Brown may make a richer black than the black pencil. Sometimes layering the very bright colors in the right order and the right combination can give richer browns and grays than using the brown and gray pencils

 •If you plan to add a background, you should do that first

 •Your pencil marks and brush strokes should go with the contours of your subject

 •If you notice an area is too dark before adding water, use a kneaded eraser to lighten it. Squeeze the eraser and press it flat against the area to be lightened. Peel it off, stretch and roll it, repeat till it's lightened. This is gentle enough that it won't damage the paper surface the way rubbing with other types of erasers will.

•Above taken from Wiki How