The RTS concept every new player needs to understand | Automaton
Talking about good RTS mindsets broadly, which would imo be enough to post it here, but he uses Age of Mythology as the specific framing device.
The short answer to the clickbait title is: think about optimising your resources collected. Idling or killing your opponents' villagers can be good for that by reducing house many resources your opponent collects, but building your own economy is the most important aspect.
I'm not sure I agree with him that 2 TC booms are the best strategy for low Elo players to go for. I've seen other creators suggest (in other Age games) that 1 TC is more useful until you've mastered the basics. I can see that he might be right that really tight rushes may not be the best way to learn fundamentals, but there's value in slightly slower 1 TC plays because they're easier to defend and push from for players without the high multitasking ability of a pro player.
Still, I think the fundamental way he suggests looking at it: as a race to gather the most resources (and, implicitly, spend those resources in a productive manner) is a good one.