I would give a depressed person the undivided attention of my listening ear. This is because the first thing to consider in depression whether it stems from a need to think out loud with someone. If it is, more often then not the person can solve their own internal struggle themselves, when given a chance to think it through. And, it is common that time is not given for a caring, listening ear that allows a person to process a struggle out loud. When all this has been provided and tried, then I have found the short-term help of an over-the-counter supplement, like St. John's Wort, to get a person over a slump; kind of like jump starting a car. Then, the person can act better on what he/she knows to do to take action.
This does not apply to all situations as this question is very broad, but it is at least where I would start.