What is the best way to help someone who is dealing with anxiety/depression?

From my own personal experience (as the one with the depression and anxiety), just having someone be THERE physically or not is HUGE. This is especially true for depression. I could sit in silence and just listen to somebody talk about anything, because I'm not in the mood to talk. But being left alone kills me. I deal with it, but it hurts.

For anxiety, mostly just being aware of the anxiety coping tactics we would learn in therapy, because when an anxiety/panic attack hits, that's the first thing I forget (how to think, about anything else). It goes beyond "just breathe." It's more like the five-four-three-two-one or something similar, proven tactics used in therapy.