On a small piece of paper draw a few shapes of objects that you can see in outline and a little darker than for transparent watercolor.
Mix up some moderately dark, warm toned brown, or brown and red with a little white in it for body. Then brush it all over your drawing, streaky if you like, or as it comes, but let the drawing show through enough to see it clearly. Then when the wash of underpaint is dry, paint the objects in their appropriate colors on top. You will be surprised at the qualities you get, and what you will find about your paint in the process.
Be careful, though, when overpainting, not to pull up your underpainting. Make sure that it is thoroughly dry. If you are in doubt about pulling up the paint, fix it with a light spray of fixative. If you don't get what you want first overpainting, overpaint it again. If it still doesn't feel or look right, draw on it with carbon, then overpaint again.
On your paper, using colored inks this time, block in a view through a pane of glass in your window. When dry, overpaint it with opaque color, leaving parts of the colored ink showing here and there where needed. The combination of colored ink and paint can be very exciting and unusual.
You could actually draw in your subject in a bright colored ink, with a brush, then fill in the spaces with paint leaving the bright ink line showing as an outline.
The possibilities of combining these media together is endless and should give you great scope for invention and for developing your style and technique. Do try them all out; you won't regret it, I promise you.
Don't forget your razor blades either. By carefully scraping off a top layer of paint you can let the underpainting peep through and so get an interesting texture.
You can go so far with the watercolor media, but there does come a point in your painting when to go any further creates havoc. Too much overpainting will lessen the sparkle and make the picture go dead. When this happens stop and start a fresh painting. Watercolors are quick to do, so take advantage of this and start again. If by some chance you feel that though the painting is dead in parts it still has qualities, give it a varnishing with a wax varnish (you can buy these ready made at the artists' supplier); they are quite simple to apply. And when dry, gently polish the wax with a silk handkerchief or fine cloth. The colors will look a little darker in tone, but the brilliance will be restored.
It is much more exciting to make your own tinted paper when using opaque watercolor, by putting on your own tint of your own choosing, than to buy the ready-made tinted papers. When you make your own tinted paper (underpainting) the overpainting merges better with it and you have the advantage of the white paper underneath to reflect back light and so give more life to the tones. Ready tinted papers don't do this and somewhat deaden the top layers of paint, giving them a rather chalky look.
Tinted papers are all right for drawing. Avoid them for painting on unless you prepare your own on white paper.