sorry, this answer will be quite long.
anyways, there's a lot of methods. but there's a few things i personally consider when naming cn original characters:
-motif/theme/personality
-rank or class (if applicable)
-importance (if applicable)
-does it sound good/ok?

using motifs or types of characters might be easiest to start with.
if your character is a warrior, you might want to incorporate hanzi that mean strength or fierceness. if they are a doctor, maybe you'll want to use a medicinal herb. maybe your character is associated with the wind, you could use the hanzi for wind in their name. or if they're associated with a season such as winter you could think of using "snow" or "cold" and so on. if they're a person with a gentle personality, perhaps you'll use the hanzi for "warm" or "soft." or maybe you can go the other way for irony, such as using the hanzi "ice" for someone who has a loving heart. maybe you have a quartet of characters and want them all to have a connecting theme. for example, using the flowers of the four seasons, so you could implement each season's flower into the separate names.

for class and/or rank, if applicable, it might be more difficult to decide. for a noble character, it's likely their name wouldn't be something common and simple such as "xiao bai" (unless as a nickname), and rather something literary or refined. poems, literary texts, idioms, etc might be a good place to start if you're feeling somewhat brave.
some families might even have a generation name. usually they're in accordance to a recorded generational poem, so common/lower class people might not use it. in modern times, generation names seem to be used less frequently but they do still exist (in fact, my cn name was decided from a generational poem).
for those that weren't nobility, it's often that names were chosen based off what parents wished for their children, or based on the environment where the child was born. for example, xiao ming as in "brightness" to wish a child will grow up smart. or even, for example, luo binghe, where he was found at the luo river. they can be really simple names!

importance, if applicable, is also noteworthy (to the point i wonder if i should mention it). although there are some ways to interpret this.
1) character importance to the story; maybe you'd want to put more effort into a beautiful or interesting name. not just for main characters but side supporting characters, or even a minor character if they have a specific role. otherwise i think it's fine to just use randomly chosen hanzi for names as long as it sounds ok/nice.
2) importance to a character, or importance to the story plot. maybe it's plot important? maybe a character takes pride in their family/clan name, or maybe a character renames themself after going through a bunch of trials.

lastly, does it sound good? easy to overlook but also quite important. you don't want a bad sounding name. of course, unless it's on purpose. such as a running gag to make fun of a character, or to be a homonym with another phrase/word to imply something, that sort of thing. it might be difficult to decide through sound, but if you know some cn then you already have an advantage over those who don't.

another minor thing is that some specific hanzi or phrases may be (traditionally) only used for men or only for women. i'll leave you to decide what to make of that.