Lots of great responses here. I love StaysFit's response!
I consider myself a mood dresser. I have in fact found that when I am feeling out of sorts, if I can find just the right thing to wear, my mood will improve significantly. Likewise, if I put something on that I don't really like for that day, I will feel out of sorts until I can change.
For me, mood dressing usually starts with the silhouette. Do I feel like I want something loose fitting, or something tight fitting? Something cozy and soft, or something crisp and tailored? Some of this has to do with the weather, of course, but some of it is emotions.
Sometimes, instead of being drawn to a particular silhouette, I'm really feeling a particular color that day. Before I open my dresser, for instance, I might already be really looking forward to wearing a particular color, or I'll know I want something light colored, or something sparkly.
If I'm choosing my footwear (after I have my outfit on), I'll scan my shoes and mentally imagine what each one will look like and feel like once on with this outfit. I might mentally imagine choice 1 as being too girly, or choice 2 as being too boring, etc. I will finally settle on the right one.
My outfit today is instructive for how mood dressing works for me. I wore a white tee, black moto, dark blue jeans, and red patent booties. I wore the red patent booties because they are made of vinyl and it looked like rain. I wore them only for that practical reason, and my heart was not in it. I felt very low on energy and would have preferred to blend in. I would have liked to have worn darker footwear instead of the bright red booties.