If you're able (you have insurance/can afford to), the single best thing you can do here is to see a professional. I've dealt with mild to moderate depression on and off for most of my adult life; four years ago my wife finally pushed me into seeing a professional, and I wish I'd done it 15 years ago. Working with him gave me some of the tools I needed to re-frame my thinking and break out of the sense of learned helplessness I was dealing with.

Meditation, diet, sleep, and exercise can all help, but ultimately it was talking to a professional that made the most difference; all those other things have helped to sustain it since then.