I've so far talked a lot about the "trigger" part of trigger-action planning (which I've often called "noticing"). Here's a tip that can help identify not just the correct trigger, but also the correct action.
“Tomorrow, you wake up to find that the thought pattern you want has miraculously established itself. What’s the very first thing you notice that’s different?”
This is called “The Miracle Question”.
The habit of thought I’m currently working on is defensiveness. At this point, all I’ve got is a trigger I’m part way through refining. I’ve studied my default pattern of thought and feeling, the one that’s causing me problems. But I don’t have any idea what to do about it yet, so this is a great time to ask The Miracle Question.
I ask myself this question via simulation, not conceptualization. I don’t just think the words or activate the abstract concepts in my mind. Rather, I pose the question by vividly imagining the experiences of a version of myself who miraculously wakes up possessing the skill I want (even if I'm not quite sure what the skill is yet).
Playing through that movie in my mind, what is the first thing to tip me off that I must be imagining her instead of me?
Ok, so I wake up. Then what? I roll over, open my eyes. I grab my phone, push the on button, and see some Facebook updates. I click through and start to read a comment where someone has criticized my idea - and this is where I feel surprise. Reading the comment, I’m still feeling just about as pleasantly languid as I was before, modulo the added focus needed to understand the comment. I feel the difference while imagining this, because ordinarily I'd respond to this situation with some sort of stress.
So what have I gained from this exercise?
I now have a concrete image of the world I hope to steer myself toward, on the scale of moment-to-moment experiences. Before, I just had a thought like "I want to spend less time being defensive." That's different from knowing in precise, concrete detail what it would look like to spend less time being defensive. I don’t know how to get to that other world yet, but I know precisely what gap I'll need to bridge: The specific change I’m after is one that will allow me to read a Facebook criticism when I’ve just woken up while feeling calm engagement.
My search for correct actions is now constrained to things that would plausibly cause that outcome - that would transport me into The Miracle World. Any potential action that would fail to bridge at least part of the gap between here and there is a step in the wrong direction.