Even if I'm working on a digital piece I'll still use pencil sketching to make quick notes. Especially when exploring the shapes of items in the scene and how they might interact. A pencil is always ready and I tend to carry a sketchbook wherever I go.
I like to draw and paint the environments that I'm actually immersed in. Planning paintings digitally allows me to take my tools with me where ever I go. When on the train or out and about in public it is much easier to paint digitally without being noticed. There's little to pack away and no cleaning up to do.
Working semi-digitally also allows me to make multiple trips to the same or similar locations and integrate elements from different days into the same scene. For "Sitting Duck" I drew each element into the scene whilst on separate train journeys. Sometimes I draw from life or take some reference images if the subject is moving.
I take reference pictures to capture particular moments, particular lighting or just capture the overall essence of a scene. The man reaching up here was a reference that I used in the final work on "Sitting Duck". I liked the lighting on his limbs but to fit him into the scene I had to move him to the other side of the train and adjust his posture.
I use a pressure sensitive wacom tablet to create brush strokes in my digital art. This gives the images a natural traditionally painted feel. I only use a simple brush, blend tool and the undo button. Other than than I use digital paint as I would any other medium.
Some images are painted digitally as the final outcome but if I am creating a piece for display I use the digital images for planning and create a pencil sketch which then forms an underdrawing for the canvas painting.