The thing about Myers Briggs is that the functions work in pairs. For an INFJ, there is the Fe-Ti pair and there is the Ni-Se pair. Some people believe you should try to continuously work on developing whatever functions you are not comfortable with in order to become a well rounded individual. However, I believe that you should use your dominant and auxiliary functions as much as you can in a healthy way, and use your tertiary and inferior functions to pull these back when you start overusing them in an unhealthy manner (especially for the Ni-Se pair). Therefore I would say this is what it would look like:
Ni: Basically look up on my blog to see what Ni means. A healthy INFJ will use their Ni so much, it’s hard to point to specific circumstances where they are using it. It’s just the core of who they are. They are future-oriented, perceptive, analytic, interested in what is symbolic, deep, and true. They approach the world, and every circumstance they can, in order to understand it on a deep, spiritual level. They spend a lot of time thinking about others’ true selves, their path in life, the meaning of life, etc.
Fe: Before the INFJ gets too caught up in a negative downward spiral of their thoughts, they have to take time to interact with others. They should take time to talk about their emotions with someone they are close to. They will also seek to help out others, caring for them, and will be very in tune to their emotions and values of those around them.
Ti: The well developed INFJ will also be able to step back from a problem when the situation calls for it, putting their emotions aside and analyzing it impersonally. They can use their sense of logic to deduce flaws or weaknesses in a situation, and can deliver criticism in a healthy way.
Se: The INFJ doesn’t overuse this function, neglecting it much more than their other functions. However, when the INFJ begins to overanalyze, project into the future negatively, or begin using their Ni in a negative way somehow, they should employ their Se. They will be able to remind themselves to take things at a surface level (in situations where they are overanalyzing), implement projects instead of just thinking about them (making sure they start step 1 before they plan out step 20), and live in the moment a little bit. They probably have hobbies in areas such as art, music, sports, etc. that they can use to develop this function in a healthy way.