Woden's Day, and Susan Sarah here....
Yesterday Pat brought up the subject of names, author names and pseudonyms, which got me thinking about naming characters. It’s a delicate thing, this picking of character names. I can spend hours–-days even-–poring over name books looking for just the right name for a character. Main, secondary, tertiary or a throwaway name, they can all impact and influence the story. That's for fictional characters--in the case of actual historical people in the book, sometimes the author is well and truly stuck, and must make the best of it.
Names can help the authenticity of a book, can help weave the fabric of that story and time period, or can undermine it and disturb the flow. Names have historical and social contexts, and those need to be considered. Some names sound very modern to our ear, despite their historical pedigree, while others are just plain ugly, or hard to pronounce, or have some social context of being frumpy or dowdy, sly or weak. The modern connotation can be as important as the historical context.
I have a big library of name books, with pages well-thumbed and liberally salted with penciling and underlining, sticky notes and printouts of additional lists. When I named my kids, I had two or three favorite books, and I still use those. Now the library has expanded to include books that list historical names and give census lists and historical background, as well as books that consider the social, numerological, and even kabbalistic context of names. Any source that helps is a good one.
Historical context is just one factor to consider--authors are also thinking about authenticity, sound (even read silently, the sound of a name is still very important), spelling, pronunciation, how many other characters' names begin with the same letter or a similar sound, and so on. For example, if you're flying through a story and need a quick name for a maidservant or a reverend, some character who pops into the story and pops right back out again, it's easy to pick up the nearest name book, choose a name, and go back to the writing. The pitfall is that if you're snatching names on the fly from the beginning of the book--everyone might begin with A, or by Chapter 4 or 5, the names start with B, and a little further on, C. *g* Of course we intend to mix up things to disguise the author process, but sometimes these things happen!
Authenticity is a biggie. Character names should fit the historical context of the story, and both sound and feel right for the character, the setting, the historical era. Many good name books will give the origin and history of a name, along with some notes on census reports showing the most common and popular names in certain centuries. Withycombe's The Oxford Dictionary of English Christian Names is one of the best for this sort of information.
A name can be historically accurate, and yet sound all wrong to the modern reader, something else to take into account. My favorite example of this is the name "Tiffany" -- if you saw this name for a medieval heroine, you might shudder at this bit of apparent inaccuracy. Yet the name did occur in the medieval era, its origin being Theophania, or Epiphany. According to Withycombe, there was a Tiffany recorded in England in 1315, along with others. It's one of several religious holiday names that were popular in earlier centuries, along with Christmas, Noel, and so on. Try getting "Tiffany" past a modern day editor, let alone a reader--!
I once named a medieval heroine "Michaelmas"--the feast of the Archangel Michael in September was her birthday. She first appeared as a secondary character, the young sister of the hero, Gavin Faulkner, in Angel Knight--both of them, brother and sister, had a natural healing ability. Readers loved the character (who was 8 years old in Angel Knight) and I got letters asking for her story. There I was, well and truly stuck with a name that would be difficult for a romance heroine. When it came time for her book--Lady Miracle, a story about Michaelmas growing up to become a 14th-century female physician--I compromised and called her "Michael," since the use of masculine names for females was very prevalent in the medieval era. 
While Publishers Weekly gave Lady Miracle a starred review (and that review is framed on my wall!), there was one memorable reviewer who bashed the book down to a crummy two-star because the heroine had a guy's name and she just couldn't get into the story.
The moral of that experience is, think way ahead when you name a character! But as the author, I loved Michaelmas, the character and the name. Looking back--I think I would have chosen the same name again.
Besides accuracy and authenticity (which are two different factors!), there's the sound of a name, the spelling, the pronunciation. Can I live with typing that name ten thousand times? In one book, I had named a character Ned -- and a few chapters into the book, changed it to something else. Writing "Ned said" was driving me mad. And while I love the name James and have used it twice (in fact, the hero of my current WIP is called James), the possessive, James's, is awkward.
I've sometimes changed the name of a hero or heroine repeatedly while writing a story. The character won't click for me unless the name is right for that character. Sometimes the name is right there from the beginning, full-blown, and other times, it takes an effort of constantly searching and changing. For example, I once called a hero Geordie--nahhh, this just didn't work for him. Geordie was a little brother, not a hero. Once I called him Duncan, the whole character sprang to life like a hologram. The heroine of my current WIP (James's heroine!) was Kirsty in the proposal, yet she just wouldn't walk, talk, or make sense until I discovered that she was, in fact, Elspeth. I will have to remind my editor not to write up any back cover copy based on the proposal....
And of course, can the reader pronounce the name --- that's always a consideration. I work with Gaelic and Celtic names often, and they are the de'il to pronounce. There are ways of gently showing the reader how to pronounce the name, by having another character learn to say it phonetically, or allowing some interior phonetic dialogue, something like that. Most of the time when I use a Gaelic name, I try to go for the ones that are obvious--like Bethoc, Morag, Niall, and leave Siobhan or Eibhlin, lovely as they are when said out loud (basically, Chevonne and Evleen), aside. 
When a character is a historical person with a tricky name--that needs to be handled delicately where possible. In my last manuscript (which will be out next year, more on that later when I have more info!), I had to work my way around Gruoch, Lulach, and Gillecomghainn--all I could do was try to simplify the names as much as possible and pray that the reader would go with it.
Sometimes the historical names for a time period are just so plain and boring--our friend Susan Miranda has had to work her way around a plethora of men named Charles, William, and James, and women named Barbara, Mary, Sarah, and Anne--bunches of them all in the same circle, and she's done an admirable job of it. No wonder, looking back over history, that men and women came to be called by their titles and properties, since so many of them were sporting the same name!
So, a few thoughts on names and naming characters -- there's much more to be said, but I have to get back to James and Elspeth, who are deep in a subterranean cave in Scotland looking for lost fairy gold, with the MacBaddies hot on their trail!
~Susan Sarah