I am reminded of a simple diagram a therapist drew for me (on a whiteboard, no less): a triangle connecting "mood" to "thought" to "behavior" illustrating how the human mental state is a feedback system and that you can adjust one thing by applying pressure to another.
Sure, it is simple and obvious, but seeing it visualized that way, coupled with the idea of "mood hygiene" was helpful to me.
The general concept is called "Cognitive Behavioral Therapy" or just CBT. One of the classic CBT workbooks (specifically for depression) is "Mind Over Mood"
Edit to add: Even though it looks like it might be, this isn't soft touchy-feely self-help bullshit. CBT has been proven as an effective treatment for things like depression. There's real science here.
The Now Habit, 7 Habits of Highly Effective People and Feeling Good: The New Mood Therapy are several popular works in this area.
Now Habit and Feeling Good both address the feedback loop we create in our own mind. Not the external pressure of life, but the internal dialogue we create around it. 7 Habits is about action steps and asking yourself "What should I really be doing."
And, for a more "runway level" approach to borrow the phrase from the next one: Getting Things Done.
EDIT: I was just about to add CBT, but I see someone beat me to it. Feeling Good is by one of the early practitioners of CBT.
Did you know that a study was done around the "Feeling Good" book, and that it was shown that merely reading it was way more effective vs. depression than antidepressants?!
(Unfortunately, I don't have the details in front of me and couldn't pull them up quickly via Google. Maybe someone else can provide a link).
Sure, it is simple and obvious, but seeing it visualized that way, coupled with the idea of "mood hygiene" was helpful to me.