Firstly, I open a new .psd file in Photoshop. It will be vertical, and the resolution will be 150-200 ppi. I generally start with a lower resolution and ramp it up later when I'm detailing the illustration, enabling me to work faster and smoother. I create a textured background before starting to draw, so I get rid of the white background. I open a new layer and start to sketch with some thin brushes, as though drawing with a sharpened pencil. I don't need to put a lot of detail into this stage, just define the general silhouette and lines (Fig.01).
Then I select the "Multiply" from the options menu of the "sketch" layer. I open a new layer under the sketch layer and start to paint roughly. At this stage, I'm paying attention to get the right colours and tones. Be aware of putting too much detail in at this stage. Try to see the whole image without zooming in much and losing yourself in details. For example, I generally work at %25 - %50 zoom level. I'll use a main light source, and two secondary light sources, making decisions on my colours and applying the temperature passes, shadows etc (Fig.02).
I continue to paint on to the layer under the sketch layer, trying to get the colours as good possible. I decide on where the highlights are to be placed in accordance with the position of the light source. As you can see, I have covered all of the canvas as I don't want to see any white areas in my image. If you leave any white spaces, you can't focus on your image and can't see it as a whole. Therefore, it's better to paint all of the canvas with at least one colour (Fig.03).