Tell Me Your Name
You write a novel. Naturally it has characters. And those characters need names! Let us set aside for some other day the issue of creating fantasy names, and consider today only naming characters with cognomens that already exist.
Depending upon how you roll, this may come very early in the writing process. In his Elements of Fiction Writing: Characters & Viewpoint, Orson Scott Card mentions a friend who gives his characters dummy names: XXX, or YYY. Only when he’s nearly finished writing does he decide on names and replace the XXX with Charles or Diego or whatever. Card adds that he himself couldn’t write that way.
It wouldn’t work for me either. For me the name comes before beginning the writing at all; if I don’t know the character’s name I can’t get any traction. I can get away without looking at my hero for many thousands of words. I was more than halfway through the first draft of How Like A God before I thought to actually cast the authorial gaze upon my hero; I knew what all the other characters looked like because I was using his viewpoint, but he had never done the old look-in-a-mirror stunt. (When I did look I was astonished, and marked the place in the text. I do like a handsome hero.) To find a true name is a powerful magic, wielded by wizards in fantasy novels. And it’s one of the core competencies of the writer.
But there are a number of factors to consider. The most important of course is time and place. A work that takes place on Mars in AD 2502 is going to have a differently-named cast than a work that is set in 1741 in Wales. Given names, especially, come and go in fashion in an easily-charted way. You can search on it and kick up sites that will graph for you the popularity of, say, John as a name for boys over the centuries. Certain names are highly redolent of their era. Consider my own. Every Brenda you are ever likely to meet is between 60 and 80, because that was when that given name was in fashion. Nearly all Lindas are the same, whereas a Madison was surely born the year after Splash and is around 40 years old today.
You therefore are foolish indeed to name your Elizabethan heroine Brenda or Madison, and if the novel is set in ancient Rome, all I can say is for god’s sake don’t! Rome, like many other cultures, had its own naming conventions which you should research carefully. Consult, if you can, actual historical documents of the period–books, newspapers, blog posts. Do not rely upon modern interpretations like movies, TV shows, or novels written after the period!