For what it's worth - and it's very weird for me to be saying so when the designer of the game is potentially in disagreement with me! but I do feel strongly about it - I see the use of moves in PbtA games as being more of an art than a science. It is, arguably, the form that "system mastery" takes in a game with this structure: learning, as a group, how and when to apply moves to your play for maximum effect.
(Notably, it's less so in AW than in some of its descendants, like Monsterhearts, but I think the basic principle applies just the same.)
How do we decide when to call for a move?
(1) Part of this is a question of a player's right to create effects and push for consequences within the fiction. You know you can 'go aggro', and thereby get an NPC to do something, so it's your right to call for that, and no one should block you - if anything, we should conspire with you to make it real and to make it happen. We just need to add enough fictional detail to the action to make it interesting and compelling and plausible. You want to do move X? Ok, let's help you make it happen - that's something you should be able to do in the game. That's why they're "your moves" - they are things you are legally entitled to as options within the scope of the game.
(2) Part of this is agreeing on what kinds of fictional events or details cause us to "trigger" moves. If someone pointing a gun at someone and yelling is understood to be "going aggro" in your game, then make that clear and be consistent with it, so we can all get on the same page. Some moves' "triggers" are really clear ("at the end of the session..."), but others require more interpretation (like "seduce/manipulate"), and you'll find yourself setting those standards over time as you play.
If don't follow some standards for when to apply moves and when not to, based on what's happening in our game (or "on screen", to use a metaphor), we start getting into some really wishy-washy territory, and I think that plays against the strengths of the game, eroding our trust in the rules we're playing by.
Having said that, however:
(3) Another part of it is choosing the best tool for your dramatic goals - how does this move, and its potential outputs, work for the fiction we're creating, the choices of the characters within it, and the dramatic necessities of the current scene or situation? There are times when this becomes key and can even override the two previous approaches - times when the outcomes listed for move X just fit perfectly for what you're doing in your scene, even though normally it wouldn't be called for (such is the case with more figurative interpretations of the moves, like "seizing the moment").
In practice, all three work together, in my experience.
A good example of the last type - a move which must be used dramatically - is the "Oftener Right" move (Savvyhead). If you try to apply its use literally, to any instance where any character is asking the Savvyhead for advice on anything at all, you'll soon be overwhelmed with notes on what advice applies where and how. And how long does it "last" for? ("Hey, I think the Savvyhead said two sessions ago that it might be a good idea to bring some food on the trip. Does that mean I can get a +1 to negotiate in the market for buying food?")
However, if you apply the move through the lens of dramatic timing, then it makes sense: we call it into play when a conversation between a character and the Savvyhead is happening and we want to lend it dramatic weight.
In other words, we use the move to mark that "this is a moment where a significant piece of advice is being given, and we want it to matter going forward". If the game were a movie, you can imagine the filmmaker might have marked it with some swelling music in the background, instead: pointing out to the audience that something important was just said or just happened.
I could even imagine a group using it more creatively: a character is pursuing her goals and runs into a real tough situation. We slow down and say, "Hey, you know the Savvyhead always used to say that no one should attempt this. Let's play out a flashback where you two were talking about it, about a month ago... now, let's get back to that scene. If you want to change your mind and turn around and run, I'll give you that +1 for realizing the Savvyhead was right after all."
That might be a bit of a stretch (I can see it being legit at some tables and not others), but sometimes this kind of thing is just the right thing to do. I can imagine a more typical example where, over many sessions of play, we learn that a certain characters always arches their eyebrow before launching into wild violence. In that game, the character arching their eyebrow meaningfully at another character who knows how they operate could qualify for "going aggro", even though normally that would be a pretty sloppy (and probably inadvisable) use of the move.
I could see a group using that for Oftener Right, too; perhaps two characters know each other well enough that they can communicate non-verbally, and that creates opportunities for a move to trigger. A character is about to leave on a journey (instead of dealing with a problem back home), and they go to their usual hiding spot, where the Savvyhead normally leaves them letters. However, this time, there's no letter there.
We all look at each other, instantly understanding what it means: the Savvyhead disapproves. What doesn't need to be said is that she wants the character to stay home and deal with the problem. It's a moment of tough love.
The player points at her character sheet and says, "I'm Oftener Right." We all understand implicitly that, should the character take this as a sign and stay back, to deal with the problem at hand, the move will apply.
That's a part of what's happening in the "shotgun to the head" example. By the book, perhaps (depending on how you interpret the 2nd Ed. rules, I suppose), we should definitely by using "go aggro" here. However, dramatically and mechanically, it makes no sense to roll dice and look for an NPC reaction when we can all see that pulling the trigger is a meaningful choice in the player's hands. Suddenly throwing in some randomness here isn't appropriate. The outcomes of the move don't help us here, either. All we care about is: does she pull the trigger or not? And then we can narrate the outcome accordingly - it's already clear to everyone what's at stake.