In the recent past I was a peer educator leading mental health groups in wellness & recovery principles, for which I received training. Getting the motivation to do anything was a very common problem. Our answer was: Start with doing a few small things; recognize and reward yourself for the accomplishments; this provides momentum to increase to bigger things; make sure to always include things you enjoy and which make you feel better (with obvious exceptions like drugs). Many of these ideas were mentioned in previous posts. Hopefully this will help.

For me personally, a big part of my depression was the burden of guilt and shame, which a couple people also mentioned. For this I found it helpful to read alot and learn the causes of disorders like depression. Learning that it was due to an alcoholic father helped me to heal-- it wasn't my fault.