Despite the name, Introverted Feeling does not refer specifically to feelings. It refers to a decision-making process that factors in personal identity, emotions and values, but that alone is not what Fi is conceptually nor does it even begin to tell the whole story.
The feeling functions interpret and understand the thing they're examining in its totality. They consider the all; the underlying concepts uniting the pieces of the whole; the meaning, the origin, the why. Introverted functions, as you know, focus on a limited perspective. They cut out a piece of reality and focus within that immediate square of perception. In a nutshell, introverted Feeling zeroes in on a singular concept and tries to discern what it means, but it's operating from a limited experience rather than a global context.
How it manifests in each of the types is entirely dependent on where it appears on the function stack. It doesn't operate on its own. How EXFPs, IXTJs and EXTJs express Fi is much, much different than the way IXFPs express Fi.
For example, a dominant Fi frequently struggles to define itself in the world. An auxiliary Fi, which supports an extroverted perceiving function, may be about recreating a perspective within oneself. Tertiary Fi can rationalize the findings of an extroverted judging auxiliary by organizing priorities, whereas inferior Fi can manifest negatively as a disdain for emotional outbursts that projects ones own fears of being perceived as weak if demonstrating emotions.
How to develop it, again, depends on the goals of all your other functions. If Ti is in your line up, you don't need Fi because you already have a function that offers you a holistic perspective (which is Fe) and you prefer to understand things in a linear, structured manner. If Fi is in your line up and it's not dominant, you can engage it more by asking WHY and what it all ~MEANS~ and what is important or isn't important about the thing to you.
In my function stack, my Fi is auxiliary. I use myself as a guinea pig and try to put myself in another person's shoes. Fi prompts me to discern what the other person is thinking, feeling, and line up what I think they need to hear to help them solve their own problem as I juggle through ideas and adjust my view as I speak to them. I'm not about emotional support so much as I am about trying to get people to think about something a different way, which is actually what I adjust my view towards first. I try to cheer them up or steer their thinking in a different perspective to match up with my own beliefs in the moment that I think will help. Unfortunately, that sometimes leads me to presume too much or makes me sound pedantic (or obnoxious).... and then get upset when I'm misinterpreted because my intentions didn't line up with what was expressed.