The main character in this concept art sketch book page is one I very much enjoy. After bringing him into existence I now have a character that I want to use in a wide array of images. That is the joy of creating concept art, you immediately start to see the world you are creating.
Using his two feeding tentacles to create a handlebar mustache gives this character a style that fits well with the steam-punk aesthetic. I imagine him a dapper chap, a family friend of considerable influence and experience. A worldly fellow, ripe with colorful tales and inner mystery. It is this imagining of the character that allows the concept art to grow and become more than the quick sketch.
Concept Art the Expanding World
Now take this world and run with, where will he go, what will he see? How will these experiences modify him? Might he have a tattoo from his trips abroad or some other adornment? So take these insights and modify and refine the concept art into another series of drawings or paintings.
Another series of items can come from something as simple as a character sketch like this; props. What items would this character have with him? Oooh now imagine his home and mode of transport, create more concept art from these ideas. Keep going, who are his friends and colleagues? Where do they hang out? I think you see where this is going.
I think the hard part will be knowing when to stop. What is too much in terms of concept art?