Tip Number 5: Underpainting
Sometimes it is a wonderful idea to give your paintings an underpainting, this can create atmosphere and feeling. Choose a colour that complements your ideas, in watercolour this will glow through and influence the whole painting.
When you are painting with such a colourful underpainting, it is very important to have a separate sheet of the same watercolour paper as the one you are using and to paint the same colour wash on it.
Then, when you are testing colours and mixes, use this spare sheet and you will get a true idea of your tones and colours. White paper would be quite false!