One of my favorite things with gouache is playing around with the backgrounds. If I'm painting something like this, I do the thing (bird) first, then the edges (where the bird meets the background), then the background (for those of you who've read my book, island to ocean, just like with oil). And if I mix different colors and then slowly start layering them, it can be super fun and beautiful. Each layer is somewhat translucent (more or less depending on the color and how much water is in the mix). I shoot for a variety of brush stroke direction, size, color, etc, because the eye loves variety. : )
See the same pelican in oil (different reference photo).