I find it interesting to read all this 'advice'. To anyone who is clinically depressed, going out with friends, doing yoga, changing the routine etc etc can be nigh near impossible. I remember when I was depressed with small children..... I could barely take care of myself and the kids let alone going out and doing stuff. And when I did get out, it made me feel even worse. Like Nath, professional help was the only thing which made a difference.
Yes, much of this advice will all help with someone who's feeling a bit down or sad. But there's a huge difference between feeling a bit low and clinical depression.