Maintaining the Enclosure

This can mean different things depending on what you're doing. Obviously a strong light source is non-negotiable if you're using paper.
Even if you're writing digitally, though, insufficient lighting can lead to unnecessary eyestrain.
It's also just plain unhealthy to sit in the dark all day!
During the day, natural lighting is preferable. If this isn't available, a good desk lamp will work just fine.
Generally I only use the Big Light as a last resort; but sometimes it also helps as an incentive. If I want to turn the Big Light off, I have to finish whatever it is I started writing— a paragraph, a chapter, a one-shot. This makes me a lot more motivated!

Sometimes you do, sometimes you don't.
If you can think of specific songs that will motivate you, whether because they're thematically fitting or because they excite you, by all means go listen to them! In the past, these have helped your workflow a lot.
But if that's not the case, lofi or ambience will probably suffice.
Playlists are really useful for this!
Sometimes what you really need to write properly is complete silence, or as close to it as you can get. There's nothing wrong with trying different things out until you settle on something that works!

To me, writing is a very private affair. It doesn't matter what the subject matter is; there's no way I'm letting anyone see a piece before it's finished, and there's even less way that I'll let a complete stranger or vague acquaintance see it if I haven't specifically asked for their feedback.
Sometimes the presence of other people doesn't bother me if there's no chance they'll catch a glimpse of what I'm doing... but I rarely feel as if that's the case.
It also doesn't much bother me if the people in question are people I'm comfortable sharing my writing with, and we have a parallel play sort of thing going on— or if we're working on a collaborative piece together. (Otherwise, their presence may be distracting, and more likely than not I'll stop writing for the time being to give them my full attention.)
Generally, I prefer to write individual projects alone.

This mostly has to do with the above points about lighting, distractions, and other people.
But your environment can have a psychological impact, too.
Writing on your bed can work if you don't have anywhere else satisfactory, but it's not ideal. It fucks with your posture; your legs tend to cramp; it's easy to lose focus, because you associate your bed with sleep and comfort rather than focus and hard work.
If you're writing on a computer or on paper, the best place to work is at a desk. On your phone, you can write pretty much anywhere, provided the above conditions are met; having that said, the floor is surprisingly nice!
Sometimes, it's a matter of feeling too exposed. This is especially true if you're writing something particularly personal or sensitive. Sometimes you need to move somewhere more isolated; sometimes this can be resolved by writing on a smaller screen or in a notebook; sometimes just turning on dark mode works wonders.
As with most other points on this list, this one is situation-dependent. Keep trying until you create an enviroment that works!

Daytime is preferable, psychologically and because of the abundance of natural light.
Late-night hyperactivity can be really useful for outlining and drafting, but it's damaging for your overall health and psyche to stay up late on a regular basis. If you are going to use this to your advantage, use it sparingly.

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