All my best work begins from little squiggles, either in a sketchbook or a computer screen, or on a napkin or a scrap of cardboard, whatever comes to hand. You can learn a lot from looking at the work of other artists, but much more from looking at their sketchbooks.
That maligned creature, the BIRO is often employed thus. You can get a remarkable variety of marks, hard and subtle from this cheap, invaluable tool.