Usually our 2D artists keep on making doodles to gather ideas from live real life study.
After lots of research and rough sketches, the character on mind is drawn on paper. Yet its only the begining stage in character designing. The character drawing has to be fine tuned again and again using lightbox and traced for final version.
The final version contains the outlines cleaned up and presented as thick and thin lines so to add more beauty and depth to the character.
From here the life of the character is turned on and his / her new world is opened from paper to digital media.