Intelligence is largely misunderstood. It is generally taken to mean processing capacity. However, it is much better understood as a combination of processing power, knowledge of rules of reasoning, and knowledge of facts.
Talking about processing capacity is largely moot because there is little we can do to change it, except perhaps for nutrition, for e.g. presence of iodine in diet can have a measurable impact on IQ. It can also dangerous to talk about it as people generally talk about incorrectly. When people talk about processing capacity, they make the mistake of thinking that there is a lot of variance in processing capacity. My sense is that variance in the processing capacity is low and the skew high. And people mistake skew for high variance. (This isn’t to say that small variance is not consequential.) In more lay man’s terms, most people are as smart as the other with very few very bright people.
Moving to the second point, knowledge of some rules of reasoning can make a profound difference in how smart a person is. Management consultants have their MECE. Scientists, the mantra that ‘correlation is not causation.’ Add to these ‘frameworks’ and rules, some general principles like: replace categorical thinking with continuous where possible, and be precise. For e.g., rather than claim that ‘there is a risk’, quantify the risk. Teach these rules to people, and they will be ‘smarter’ as a result. Lastly, ignorance of relevant facts limits how well one can reason. Thus, increasing the repository of relevant facts at hand can make the person smarter.