1 Sketch and values
I sketch out an idea and then add details, paying attention to composition, anatomy and design. Then I create a duplicate of my file (Image>Duplicate) and merge the layers (Cmd+ Shift+E). I increase the size of the picture, making it no bigger than 800px wide, so neither my computer nor Photoshop will lag. I paint the main shapes in greyscale.
2 Develop a colour scheme
When I think the balance between black and white is correct, I add colour to my sketch. My aim is not to have something precise, but to get the harmony right. I limit myself to three main colours, and then play with Saturation. And to avoid being distracted by details, I blur everything using Gaussian Blur. This means I stay focused on colours and composition.