One of the simplest ways of achieving a harmonious watercolour is to use a limited palette. A really useful exercise is to paint a number of colour wheels using 3 colours so you can instantly see which would be the best choice of colours for your painting. As you can see from the colour wheels below some may be more suited to the English landscape, others would work better for say a Mediterranean scene.
Cadmium red, ultramarine and yellow ochre
Cadmium red, ultramarine and cadmium yellowLight red, ultramarine and raw siennaAlizarin crimson, ultramarine, and raw sienna Ultramarine, burnt sienna, and yellow ochreCadmium red, ultramarine and yellow ochre
I think you will agree there’s nothing boring about working with a limited palette.