I find myself working in sketchbooks quite a lot these last couple of years. I mean besides the portrait books which are ongoing for decades, there are now books dedicated to the exploration of abstract imagery and ideas.
Here are a few images from the Blackbook 6x8"...
First I close my eyes and draw the lines with various sorts of markers and pens, then I open my eyes and colour them in with acrylic paints, sometimes gouache.
The very repetitive process goes a long way toward developing the visual language.