Start with wetting the whole page. I watered down prussian blue and with a 1" flat brush, lightly touched in the trees in the background and the larger back trees of the foreground. Touch a thirsty brush into your background trees to create negative shapes. As your paper starts to absorb the water, start strengthening your color by allowing more pigment on the brush to touch in darker and darker values.
After you've laid on your lightest (most watered down) colors and your mid tones, dry your painting and go back in with your darkest darks, softening some edges and leaving some edges hard. While your trees are still wet, scratch in some branches with a toothpick or whatever it is you use to scrape paint with.
Practicing with a color value painting is important for a watercolor artist. It helps you understand the entire depth of one color and how to use that color with differing amounts of water.
Try it and have fun!