How do you maintain a positive outlook when dealing with your own depression?

You don't have to: Lots of varying opinion on this, and what follows is just one. Rather than judge & try to avoid neg thoughts (especially during a depressive episode), it might be better to simply accept them, and perhaps even find meaning in them through various ways: psychotherapy, meditation/reflection, journaling, etc. Negative thinking isn't something to avoid altogether--antithetical to our western paradigm.

Get support: When depressed, we really need the support of others to help us maintain hope. Depression produces changes in our perceptions, where we over-focus on painful things and may completely miss positive things going on right in our midst. Good listeners can provide helpful feedback, adjusting our vision when it gets too dark. So, please don't do this all by yourself! doctors/therapists help too.