First, I laid down the line work. I did this with a Platinum desk pen filled with Platinum carbon ink. The ink dries really quickly and is pretty waterproof. This is important for me as you can see from the next step.
Next, I start laying down some colour. I use a Pentel Aqua Pen filled with dilute Windsor & Newton ink, which is why waterproof ink is important to me. I don’t want to smudge the lines about. I start with the lightest colours and work my way up to the darker colours. I don’t mind going over the lines a bit.
I continue putting down colour until I’m fairly satisfied that the colours are where I want them, letting them dry between layers. In places, there are probably about a dozen layers. That’s it, really.