The Ask-A-Witch team takes depression very seriously because it's not only an emotional/mental problem, but a chemical one as well. Please read our article on Depression for more information.
A ritual incorporating the goddess Kwan Yin (compassion) and the god Ganesh (remover of obstacles) has worked for a lot of folks. A lot of images of Kwan Yin involve her pouring healing waters, so anything symbolizing water would work. As for Ganesh, an elephant image would work (as he is the Hindu god with the elephant head). I would also recommend using a pink chime candle for Kwan Yin and a yellow chime candle for Ganesh. You can use a rose quartz gemstone for reducing the depression and a carnelian for motivation and moving forward. You'll charge them during the ritual and then carry them with you once the ritual is complete. Go from the heart when writing the ritual itself; it doesn't have to be complicated, just meaningful for you.