The (Step) Ladder Of Intelligence
The first rung of the ladder is, I think, noticing. Then asking questions about what you've noticed. After that it's basically just habits. Those are the fundamentals.
At the top level of the step ladder things get more complicated: skills and meta-skills. But those are really forming habits of applying certain patterns of thought to what you've noticed. Maybe it's about asking certain questions, or doing certain logical steps. Just following a recipe, really.
I'm not actually sure if there is anything fundamentally beyond that. It's about working with your abilities to just do the most that you can. Not holding yourself back- that's just noticing and questioning again. Maybe doing it faster, reflexively. Discovering or learning a new skill.
Kind of a relief to know that this is all it is to being intelligent. It's a process, and you can focus on just doing the process better.