In any pursuit
I’m thinking swimming here, but this philosophy can apply to many other pursuits.
First , focus on doing it non-stop. Go slow enough that you can do that, then increase the time you can. After that, it’s a matter of building on your technique to increase efficiency. And that’s it. From then on, that’s all you’re working on. Building efficiency, and working to go longer.
The non-stop part is easily overlooked. You need to know what it feels like to do the thing for that length of time. But once you do, all that’s left is doing the thing, and focusing on those 1% incremental gains.