I love this topic. I collect names. You know those lists of donors you sometimes see in concert programs or on display boards at museums or etched into bricks in parks? I browse those and write down names that sound interesting to me, both first names and last names. Movie ending credits - especially modern ones with crews of thousands - are another great source of diverse and interesting names. I have one character I named after a football player - I’m not especially a fan, but the game was on while I was sketching some chapter, and I liked the sound of the name. I cut the -ski off the end and used it.
The novel I’m working on is set ca.1950 so I spend a lot of time perusing various sources of names that were popular to give to babies in the 1920s or 1910s. That’s not to say that everyone is named Mary, Mabel, and Richard, but if you go down a few dozen names from the top of such a list you can find great names that have the right old-fashioned feel without being the absolutely most common names. You’ll find names in my book like Grace, Shep, Harry, Claire, Charlie ...
I had a sort of “Greek chorus” of minor characters - a group of friends my main character spends time with - and in early sketches of the novel I just assigned them the first names of the Go-Gos: Belinda, Kathy, Jane, Charlotte, and Gina. I was being silly, but as it happens all of those names have the right period feel and so most of them have stuck.
I had a character who was partly inspired by a character in another book who had a name from Greek mythology, so I gave my character a Greek-myth name too. Other characters I have just baldly named after the real-life or fictional people who inspired them. One character is named for a real-life friend I modeled him after. Another is named for a nom-de-plume once used by a certain author who inspired me.
So much for collecting names. The other piece, of course, is matching the name to the character, and that’s less systematic, more a matter of feel. I like names that add layers to a characterization, when I can find them. That’s why I was so delighted when I hit upon the name Grace for one of my main characters; she is aptly named. I think about who the character is and what I want her name to signify about her, and I look for a match in my sources. For example, for my other main character, I wanted her to have a tomboyish name, and the era had plenty of those to choose from - I landed on Eddie pretty quickly and just knew it was right, so I named her Edwina.
For her last name, I looked to the story I was creating for her. She is part of a prominent New York family, and I wanted her name to evoke that. It also needed to be distinctive, so that when she gets in trouble in the book, people know who she is enough to cause a minor scandal. So I opened up some New York maps, and looked for names of old towns around the Hudson, street names, and other names that one might associate with New York going back many years. I landed on Gansevoort, which is the name of a street in the West Village - and there could not be a more perfect name for this character than Eddie Gansevoort.
Like I said, a favorite topic. You pulled a string; I can talk about this at great length.