I'm asking with an open mind here, and knowing two things: just telling yourself "you need to be more social" has, if anything, the opposite effect. And God, do I remember hating the feeling. And the second: I did it. Wasn't a huge difference, but went from mostly INTJ to mostly ENTJ over about 20 years. Unfortunately, 20 years is too long to be able to put my finger on something and say "this worked". If I were to give a hint, I'd say that context matters. Probably the most dramatic change was from being literally friendless for a few years to hosting parties, simply because I found a social group with common interests (and very common flaws). Also in the context category, I'd say competence helps a lot. You know that "Hermione" stereotype where you can only interact with people by helping them? It actually works. It takes many years, but eventually helping should lead to "working with" and eventually to "leading". Mind the "many years" part though.