I believe that no matter which personality function a person is trying to improve, they are going to be growing. But these are some functions where they are already good enough, so there is a diminishing return to improving them, like the dominant function. Some of them might be harder to even start on. At least for me, the trickster function is like that.
I don't know for other people, but from my experience, the best way to improve is to let the second function out to play.
I notice the difference, because I remember when I started to relay more on my Ne, than on my Ti. And that was when I had my study exchange in Germany.
The reason was that before that I did not really needed to use it. Living in my home town, being part of the regular communities, living my life, it all just made sense. I had, through my life, observed and created a mental model of what was needed for a normal life.
Then I come to Germany. I got lost. Then I had trouble using an ATM, because the card has to be turned in a different way. I was not the only person having problems with it, as I later encountered two Greek students that had the same problem. I had no preexisting social life. I had no idea how the faculty that I was attending worked. Hell, I lived with two other women and when I came there I had no idea what the rules of living together were. Not to mention, the pamphlet with the process of how to connect to the internet could just say to use ssh, instead of a complicated process, that only worked on Windows.
Ti can be a pretty good analyzer, but it needs data. In order to get data, an extraverted function has to collect it. So what my Ne did was to start looking for a different possibilities of what is possible around me. Then it pushed me to try it.
Then the results were analyzed by Ti, and in about two to three weeks I was already so confident in my surroundings, that I could live there for the rest of my life.
But after these couple of weeks, I did not really get back to the old path. At least no entirely. I liked the experience so much, that I have tried to incorporate it into my life in a more active way.
It is that experience that allowed my to start a lot of projects in my Toastmasters club. It was that experience that pushed me to go to a summer school with students from Faculty of Computer Science, even though I at the time studied at the Faculty o Economics and was only doing little programming for fun. It was that experience that allowed me to make my time studying a lot more flexible. If not for that experience, I most likely would not be writing this blog either.
For me, allowing the auxiliary function out to play was the most growth like experience that I have discovered so far. It does not compare with my experience trying to improve Fe (my anima), which, while it was helpful, it was the most stressful thing. Or my Si (my eternal child), which is sometimes kind of boring and sometimes fun. Or Te (opposite personality) which was just frustrating with no payback. Or Se, which just did not help so far.
It was Ne (auxiliary) that was not only fun and exciting, but also the one that made me a different person that I was before.