Soundproof everything.
In all seriousness, noibat have extremely sensitive hearing, far more than any other pokémon. The first thing you’ll need to do is ensure it has a nice, quiet place to go, preferably one that’s as dark as possible and definitely if you live in an urban environment. Basements tend to be favored places, as the dampness can remind a noibat of its home cave. The larger this space, the better, as you’ll want to give your noibat plenty of room to fly about or roost. Also, just because you’ll want a darker, damper environment for your noibat does not mean it should be cold. In the winter, be sure your noibat’s living area is just a bit warm. If the space is too cold for you to go about without a jacket, then it’s too cold for your noibat.
Besides that, unlike mice- or rat-like pokémon like pikachu or rattata, noibat need minimal direct care, as they tend to be wilder than its rodent cousins. Giving it a soundproof space that you wouldn’t mind cleaning frequently (as in, once a day), as well as sources of food and water, are really all you need to do. Remember that noibat are frugivores, so have plenty of berries on hand for it to eat.
Your noibat will self-groom, so providing it with something to bathe in—even a sand bath—is not necessary unless it’s ill, covered in something poisonous, or particularly dirty. Otherwise, although it’s fine to groom your noibat to build affection, this should only be done after the two of you have established trust in each other—and even then, only occasionally. Noibat are largely independent pokémon, so many of them feel uncomfortable when touched by humans unless they initiate contact themselves.
Ultimately, that’s the main key to taking care of noibat: remembering that many of them like their space. Unless hatched from an egg and raised by hand as a hatchling, noibat are shy, skittish creatures in comparison to their rodent cousins, zubat and woobat included. Always let your noibat come to you if it wants affection or to be touched in general; never force your noibat to come to you. The more you show it that you’re willing to give it the space it needs, the more likely it will trust you and feel comfortable around you (paradoxically enough). You’ll know when you’ve built a solid relationship with your noibat if it comes to you frequently and lets you pet it or give it affection for more than a few minutes at a time.
As for your second question, the process of preparing for evolution is more or less the same as it is with any other pokémon, really. If your noibat expresses interest in evolution, be sure to support them but also verify that this is absolutely what they want to do. Then, start your noibat on a daily training regimen consisting of at least one hour of training per day. Flying exercises might also be something worth considering, that might make your noibat’s transition into its noivern form a lot smoother.
Of course, it’s important to keep in mind that noivern are dragons, not only at heart but also very, very literally. For one, they need a lot more space than noibat, but at the same time, their requirements for a dark, quiet living space is just as important for them. (Hence, basements tend to be even better ideas for keeping them.) Additionally, as draconic pokémon, they’ll want plenty of opportunity to exercise and fly about, so it’s a good idea to maintain your training schedule well after noivern’s evolution. It would also be a wise idea to construct a noivern door connected to its usual living space so that, at night, your noivern may come and go as it pleases and get additional exercise on its own. (For that matter, it would be a good idea to speak with Nurse Joy prior to evolution about options for implanting a chip on your noibat.)
Finally, as noted in its entry, despite being draconic in nature (in that they prefer their freedom), noivern are generally either fiercely loyal or shy around humans. Which yours will be tends to depend on the care you give it prior to evolution. If you’ve reached the aforementioned stage where your noibat will come to you frequently, then it will likely evolve into the fiercely loyal sort of noivern. If, however, your noibat for any reason doesn’t feel comfortable around you by the time it evolves, it will most certainly grow into the sort of noivern who prefers avoiding contact with humans, including you. It would be important, if you end up with the latter sort of noivern, to change your habits and work to build noivern’s trust in you. It’s not impossible to do so after evolution, but it will take a lot more time and patience, as it will require you to give your noivern enough space while also providing it with a reason for it to come home at the end of the night.
I do hope this all made sense, anonymous. Noibat can be a challenging pokémon to handle, just because their normally shy disposition makes them difficult to tame. Nonetheless, as with all pokémon, patience is the key to gaining a lifelong friend.
The Pokédex According to Bill 