How to Help Depression

A really close friend of mine is depressed and is on medication and seeking help, but some days it is really bad and lately it seems he is more depressed than usual. I know things have been rough for him but he turns into this huge jerk when he gets really low. Than he'll drink and be a complete problem. I really care for him and want to be able to talk to him and help him when he's upset. He wants to yell and take things out on me but I don't want our friendship to end, we've had so many good times and I think he needs a friend now more than ever.

How do I console someone who is depressed?

What do I say when he rambles on about hating everything and everyone? I try to approach cautiously but I never know what to say. I don't want my friend to overreact and do something crazy. How do I talk him down when he's in that really bad place??

I need to know how to deal with his negativity. Please help!!!