good question! in general, i try to keep things transparent and light as long as possible -
i have a tendency to get really dark with my watercolors relatively soon into starting the painting, so i kinda have to keep myself mindful of how the overall pic is turning out.
my rule of thumb is to keep the values balanced evenly across the whole picture as you start, and as the broad hues are laid in (in this case greeny yellow), begin adding colored shadows with ultramarines, reds and violets to increase the value curve.

if all goes well, i only have to add eyeball highlights or little touches with acrylic on top to make it "pop" - but that's a balancing act too - thick lights in opaque paint on top of transparent watercolors can look sloppy if you don't approach it with a delicate wrist. X_X