Have you heard of negative painting? It's a way to create stunning depth and dimension in your watercolor pieces by first creating the outline of the shapes you which to draw and then painting the darker background first. The foreground is painted last which creates gorgeous layers in your work.
Chuubibi illustrates the technique in the video below. All you'll need to follow along is a set of watercolors, brushes (in this case water brush pens) and some black fine line drawing pens.
Art-n-Fly Black Fineliners: https://www.artnfly.com/collections/pens/products/fineliner-inking-pens-set-of-6-tips
Art-n-Fly 72 Watercolors (water brush pens included): https://www.artnfly.com/collections/paint/products/72-watercolor-set-ultimate-set-with-metallic-pastels-skin-tones-and-other-vibrant-shades