Diffusion: gives the medium a certain amount of wetness, usually use it for the base color on big areas as well as to give a blurred effect at places.
Simple water: my most used tool from watercolor, most colorings are done with this.
Papers: base's textures, doesn't really stand out used with watercolor brushes, but for rough textures like rocks and machines, I do increase the percentage, but for skins just usually not at all.
Controls - size: used most frequent during coloring, shortcut keys are [ and ] on the keyboard, adjusting the brush sizes from time to time gives better control over the color mixings.
Controls - opacity: I usually keep the brush opacity at 100% because personally I like my colors a little more opaque, though it does make using watercolor a little not like it in some ways.
A tablet is a must, I use a Wacom one. Without one I'd recommend users to stick to Photoshop because in my point of view without a tablet it's really difficult to work in painter.
01, 02 - Coloring should always begin with the background, usual steps are to decide on the range of basic colors to use, shade blocks, then go into details. In this picture I wanted to present something simple and at will, so in the lighting and colors I didn't apply the aforementioned method, instead, directly into section by section of details.
03, 04 - Behind is a huge robot's head. After laying out the base colors, follow the value and tones to define details. Some cracks and scratches were added to the surface to give more texture.
05 - Finishing the background, I started working on the girl. The face takes a lot of time to render. Detailing the light pupils and dark eye rims, the forehead and face's sides' textures, all to give her a more industrial feel.