Oh those troubled friends

I always find it best not to intervene unless I am asked or it would be dangerous not to (and by dangerous I mean the other party is severely depressed and might need medical help).
When I say 'asked' I mean they start telling me how they feel, I find it's important not to pry or try to get them to 'share' with me, because that usually makes it worse before it gets better. A lot of the time people just need someone to talk to to help straiten things out in their head. Always remember, there is only so much of yourself you can give for another person, and if it starts to drag on you I suggest you be honest with the other person. Tell them you are only good for so long or get some extra help to for your friend (could another friend, or even a psychiatrist [nobody likes the idea of a psychiatrist, but they do help in some cases])
When dealing with yourself it's a similar story, take your time with your own emotions to understand why you feel a certain way, and if you feel to confused to sort it out by yourself thats when you should talk to people. Always remember it always gets better eventually, if you were happy all the time happy would lose it value and life would be nothing.
-I hope that helps and doesn't just sound crazy...

Jam it back in, in the dark.