As of thinking of one thing only or focusing you shouldn't. Because then you could have something and then work even more on those details and stuff. For inspiration and more experience you could make things that is in your surroundings or objects, even the smallest things can become big things in your ideas. Writing, projects even games need brainstorming and concepts for characters so that you can be sure of the idea deals with that specific creation. Asking questions is one thing that makes use think but what we what is not game we build but what emotions should we character for the players to feel during the game. Once you have the core you can then have the work of what makes the core. So meaning that once you have concept of your game then you could branch off and commence doing the characters, environment, and others. There are many ways to make the players feel something by color of the scene or the colors that the characters wear. Oh it's a block...well it can be a giant robot. When something or an object makes you think about how it can create a character go for it and make it work. I guess that's what thumbnail is, since I guess you just sketch it out. And if the sketch doesn't go along with the concept then save it for future ideas for a game.
When creating characters you would need to see what type of eyes or clothes, etc. does this particular character wear or have. Because for me that means what makes them different out of everyone. Also think about where and probably when the character is because then the character would be able to make sense upon where he or she is. Shapes are what makes like the outline of characters. They would also make emotions upon which shape you use like for me a circle is like a clam, smoothing person while a triangle is like a bold, hardcore person. Angles are what makes it more pop-out mostly on a silhouette it's important because then you could see the type of character. Of course creating characters can take time but when you show it you can have feedback or maybe something else.
I could use these techniques mostly the practice upon drawing anime because I would want to be better on creating characters that show some sort of emotion. Now since I usually sketch on paper it's going to be harder for me to draw digital which all game characters are going to be created I'm sure. But also now I would see to what type of colors, or like shapes, etc. to use when I'm creating character art. I would probably even brainstorm even more or like see about to my surroundings to create and bring ideas that I could use later in life. Also I will keep in mind about what would this make the player feel mostly I would presume because of the color or how characters act or something. I have lots to learn about this concept but hopefully I will learn more during years of adventuring and stuff.