People often ask me, how do I develop (this) function? Or, how can I bring all four functions into consciousness? These questions, light as they may be said, are quite heavy. When we talk about type, we are not talking about a mere skill one can develop; it is the very essence of our phenomenology. The above questions are akin to asking for a transformation into a different person - and that is something many people are hesitant to do. It is also something difficult to do, for those who achieve it.
If you are an FiNe and you wish to develop your Te, you will have to come to change your mindset about Te, understand its values and come to change your own value structure and sense of self so as to align with it. If you succeed you will not be the same person on the other side. In a similar vein, those who have non-standard developments (that is, a subtype other than the primary function) often have come to that development due to extreme environmental conditions. Similarly extreme conditions are necessary to do the task deliberately.
If after hearing this you are still motivated, perhaps because you seek to become a more whole person, or have strong flaws of character that you wish to overcome, then I would recommend you:
It's in the nature of function polarities to devalue each other. Perhaps the first step that's needed before integrating a function is believing in the merit your functions have, and in what form they are "right" about what they say.
Values of Ne > Si
Ne will view Si as stuck in the past, old, outdated, with no new vitality or anything to offer but stagnation. It is the ultimate submission into the mundane, and an end to chasing dreams. To grow into Si may feel like 'settling' for what 'is' and to cease the chase of the 'yet to be' - something very painful indeed. But Ne must come to accept the specific life that one's been dealt, and to see that what one already has is beautiful and enough. I would recommend Von Franz' book Problems of the Puer Aeternus to anyone suffering from a need to develop Si.
Values of Fi > Te
Fi will look at Te as militant, insensitive, and cold. Establishing a set of impersonal procedures to handle human beings may seem like reducing individuals into numbers/automatons; a deeply insulting proposition. But sometimes it's necessary - for the conservation of Fi's life principles - for Te to standardize a system which can output helpful solutions for everyone. But such a system calls for people to manage it in a dispassionate way. If it's understood that systematization can work for the benefit of life, the value of working hard and thinking mechanically can be appreciated.
Values of Ti > Fe
Ti will look at Fe as full of hot air, dishonest and emotionally manipulative or exploitative in its rhetoric. It may view Fe as prioritizing its social rapport above integrity to truth. But Ti must come to understand that truth needs a delivery agent for people to rally behind it and believe it. A dispassionate argument, however true, with no life or vigor behind it will not move and change the hearts of people/society. If Ti is to be effective in altering the misconceptions of others, it must come to appreciate and develop the talent of persuasion and learn to use it nobly and with a good conscience.
Values of Ni >Se
Ni will look at Se as jovial, trivial and overstimulating. It may not see the point of recreation and look down upon those who spend their life exclusively in the contemporary world, rather than thinking about the timelessness they are a part of. When the thematic seems like the most 'real' because it's the most lasting/enduring and eternal, the temporal may feel like just a small instance - soon to change while the pattern remains. But Ni must come to appreciate their specificity as a human, and how they are indeed one person - not a pattern - experiencing this one event in time. If Ni can come to appreciate their connection to the finite present (which must be taken advantage of), suddenly the thought of maximizing their quality of life becomes necessary. Living in direct contact with this radiant life becomes the only sensible thing to do in a world where, at every second, we only have the present moment.
Take a look at the traits of the functions, and see which ones you embody. Chances are you'll have at least one or two of the qualities of even your lower functions. Next time you display that trait, make note of it as well as the feeling surrounding it. Let that feeling sink into your bones, and internalize the perspective from which it comes from. Become, for a moment, that perspective and live a little longer through it.
Pick out one of the other adjacent traits of your function and explore it. If you have a need to explore your Si, you might visit your grandmother and ask her to tell you anything she can remember about her own grandmother. Try to connect to your roots and track down your genealogy. Or if you have a need to develop Ti, sit down with a pen and paper and write down the one thing you know deep in you to be indisputably true. Try to debunk it. If you do debunk it, come up with another. Try until you are left with something you can't debunk with sterile reasoning. Write down as many of these essentially true premises as you know, and connect them together causally until you have a logical scaffold that you can stand with conviction behind.
Take a peek at our database for those who have that function as dominant, and look for the books they've written. Look until you find one that draws your attention and buy/read it. Often times they will write from the perspective of their dominant function. Here are a few such books that reveal the epistemology of each function, and lay bare its value/virtue:
Whether it's Fe-lead Tony Robbins and his "Awaken the Giant Within", or Ni-lead Rupert Sheldrake's "The Science Delusion" - every book will inform you as to what it's like to think from the perspective of that dominant function.
Last, but perhaps most importantly, find a teacher. Whether it's a friend or colleague - if someone with that function developed is willing to teach you the skills they know, don't let the opportunity pass. You don't necessarily have to enter a formal student-mentor arrangement with them, but study them and how they do things then try to imitate their strategies. Set a goal for yourself to be better than them or to be able to compete at their level in at least one facet of their development.
At first using lower functions will feel like a betrayal of yourself and all you stand for. If it doesn't feel that way, you're not exercising it properly or adamantly enough. However, you'll know when your function is coming into consciousness when you no longer feel that way but begin to enjoy the activity for its own sake and even start to initiate it. When a function is conscious, the energetic toll felt by using it should be akin to having done a workout, rather than battling against all that you are.