It usually takes destroying a half-dozen attempts to get one to turn out, and that by many professionals. The imidiacy and spontaneousness of watercolors demands control and proficiency.
My recommendation is to mess around watercolor as washes of color that fill drawings or sketches. Get a sketchbook, and just begin sketching objects in any room...of anybody, any thing. Use a BIC ball point black medium pen...use charcoal pencils, use sepia colored pencils...whatever- for drawing. Then use watercolor loosely and in washes of color...hhmmm...staining the drawings with color.
To get that sense of spontaneousness, don't labor over the drawings. Do them as quick studies...gestures..sketches. Then fill with color, and you can always go back into the colored drawing to beef 'em back up with more drawing tools. peace, Larry Seiler artist's site-
http://cwinc.net/larryseiler WetCanvas Artists page- (shorter and quicker loading)
http://www.wetcanvas.com/Gallery/S/Larry_Seiler/
index.html 'The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.' George Bernard Shaw