I can't think of much to add to what Coonlight said. For me being physically active and getting outdoors is key when I'm in a dark mood. And, I try to avoid being alone too much... which is against my instincts because I'm very introverted and usually the last thing I want when I'm struggling is to interact with people. But I find that if I spend too much time alone when I'm depressed or anxious or angry, my worst thoughts start building on each other and send me further into a tailspin. Interacting with somebody helps stop that spiral.
And I find that it helps to do something that isn't consuming media (whether it be reading news articles or internet message boards or watching TV.) Write a story, draw a picture, do a crossword puzzle, or so-on.
And, do one of the little tasks around your home that you've been putting off. Accomplishing things, no matter how small, helps fight off the feeling of hopelessness and futility. When I feel I like I am floundering, I force myself to do *something*. Vacuum. Clean the bathroom. Clean up the stack of clutter on my kitchen counter. Anything. A piece of wisdom that one character gave another on the Stumptown TV show is "Make your bed." It turns out it actually came from a US navy admiral named William McRaven, who said: "If you make your bed every morning, you will have accomplished the first task of the day. It will give you a small sense of pride, and it will encourage you to do another task, and another, and another. And by the end of the day that one task completed will have turned into many tasks completed."
-k