I hope if you know someone with anxiety or depression, you realize that they're not just choosing to feel that way. I can't really explain it, but for some reason, you can't choose to just "snap out of it." It's not just a bad day or a bad week, it is, as Elder Holland stated, "a crater in the mind."
I guess one small bit of advice I can give is that if you have anxiety or depression, don't feel guilty about it. I realize this is easier said than done, but try to remember that you aren't choosing to feel this way, it is just something you are dealing with for a time. Do your best, but realize your best may not be as much as you wish it could be at the moment. Remember you are doing the best you can and you should never feel you are a bad person because of your condition.
I remember when I was feeling very deep feelings of depression, I would see bubbly or enthusiastic people, and almost feel angry. I knew I had been a happy person who saw the glass "half full." At this time though, I felt like my class wasn't only half empty, but completely drained and dry. I felt guilty when I would see people enjoying life. I figured I was being ungrateful and letting my life waste away. As I've learned more about depression, I realize that you shouldn't ever feel guilt because of it. Just like the flu or diabetes, it doesn't make you less of a person, it is just something you experience. While I still have hard days and I can't say I am "over" depression, most days I can see the glass half full (and maybe even full to the brim!)
To read Elder Holland's full talk, click here.