The biggest issue I have when designing adventures is the same one I have when designing characters as a player: naming them. I know what I want their skills, history and personality to be, because that all has a tangible effect, but a name can be anything. If it can be anything, how do I narrow down what it SHOULD be?
It gets even harder when designing adventures with multiple characters, all needing a name. I can't share names and have fifteen Jims, but I don't want to end up with the three human tavern owners Jim, Nunzio and Kxarbutlko. Different names that sound like they fit together... Very tricky, personally.
And I don't wanna just use foreign words, because I live in fear of the day when a Spaniard asks me why I named a villain "cabbage" or something. And it's surprisingly hard finding a relevant word that actually sounds like a decent name.
I think names are surprisingly important — they establish the atmosphere of your world just like background music sets the tone of a film.
I generate random words using an online tool (recently I've been using donjon.bin.sh). For my world, the fantasy names are too "tropey", so I use the Markov Chains generator (Markov Chains use source text to structure the random syllables it generates—if your source text has no Zs, nor will your random words).
In general (but not always) I figure that short, one syllable names are most suitable for nicknames, or for common, lower class names. Two syllable names tend to be typical, ordinary people, three syllable names are more well-to-do, four syllables names are more high-class (or pretentious) and five or more syllable names are very exotic—probably foreign dignitaries, wizards or sages. (They'll probably have shorter names that friends actually know them by—if they have friends!)
Place names are just as important—in fact, even more important! Often place names contribute to someone's name, or a historic person's name can become the name of a place.
Similarly, the names of Gods and Goddesses are vital. Get them wrong, and it'll skew the whole vibe of your setting.
If you like, you can get creative, and make name words for particular regions have a particular character. Grab a source text for your Markov Chains that has the forms "kn" and "gn" in a lot. Okay, that's one particular area. Use the combos "dz" and "dj" for another area.
Maybe have one area where everyone who's male has a name ending in o, and everyone who's female has a name ending in a. And, of course, the residents of that area will add o or a to the characters' names—because that's the rule for names!
When the PCs meet someone then they should, eventually, be able to guess their approximate social status, the region their family comes from, their religion, and maybe even their current place of residence—just from their name!
And yes. People's names can change over time! Part of them will stay the same, but part may be to do with their profession, their home or something they're famous for.
I tend to find my "hit rate" on suitable names is only about 2%. Most random words aren't easily pronouncable, or just don't feel right. So sometimes I'll spend a half hour just generating names and saving them off in a list. I don't know what the names are for yet, I just have them on the side, then slot them into game sessions as appropriate. Yeah. I almost never use more than 25% of my name lists. So I generate more!
And pro-tip: some regions may have default names. In medieval England, loads of people were just called John—meaning, "You! Unimportant person!". John Smith, John Miller, John Farmer, John Wheelwright… And even if that wasn't their actual name, if that's what his Lordship calls you, who are you to argue?