Well, I think you should always just look at the position without thinking so hard, just look around.
The reason you can solve easy puzzles in 2 seconds is because you see the answer through intuition or pattern recognition.
The issue with each of your categories is that you need intuition to guide you. For instance, how do you know what the opponent's threats are? How do you calculate when there are so many candidate moves, and more possible responses? How do you know when to stop calculating? How do you know when there's a trap?
It's really all about intuition. It explains why Hikaru can find tactics in 1+0 bullet that a lot of players can't find given 30 minutes to analyze the position.
Please (constructively) criticize my initial draft so that I can improve it. Copy/paste it and print it out if you find it helpful.
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Systematic Puzzle Solving:
Additionally, keep in mind what you are looking for:
Tips and Considerations: