If I were to jump back up to the elf statement I made earlier - my mood board might be filled with images of acrobats, athletes in motion, natural motifs and patterns, successful WoW characters, various types of armor or weapons (real world and fantasy based), textures, patterns, metal samples, natural items (leaves, leather, etc). The items that go on the board aren't there to define an solution - they are there to serve as visual cues for questions we are asking while we explore the challenge we set ourselves.
Some common questions I ask myself in this exploration phase:
Who else has answered this challenge in the past?
What have others done in the past in response to this challenge?
What explorations did those answers generate afterwards?
Where can I see examples of this challenge?
Who am I trying to reach with this challenge?
What do they find important/valuable?
How do I want them to feel, or what action do I want them to take?
What colors/textures come to mind when I think of the challenge?
What music comes to mind when I think of the challenge?
I'll ask tons of questions, and try to find images or items that visually answer my questions, and put them on the wall. By the way, write down all your questions. They will come in handy later. When I've got a wall of goodies, and when I've answered all of my questions in a visual manner, kind of created a visual representation of the challenge, that is when I will finally sit down and see if I can find the answer to my challenge. I start to sift through the visual information - look for answers, visual solutions, white space or ways to differentiate myself from my competition.