Shapes, color, concept: where do you usually begin when conceiving a design?
If I'm doing a design that refers to "X", I will spend as much time as I can allot to learn about "X". Usually, when I've done this research an idea of the path I am to take has began to form.
When I am stumped on something I just flip through design books until something I see triggers an idea.
Still, the idea can come from anywhere so the key is to stay open and aware of the world around you.