So you’ve finished your novel, your characters are fully flesh persona’s in their own right, and each has a unique voice and presence. That is awesome!
Less awesome is the fact that they’re called Tammy, Timmy, and Tony. A similarity in names that is guaranteed to disrupt the flow of the story as your reader goes back to double check who said what. Was Timmy the one with the limp and the gift for magic, or was that Tony? Has Tammy had a sex change since chapter 3 that the author decided wasn’t important enough to mention?
So, easy solution, put all your character names on a single document; nothing but name. See if the names are visually similar, if so you might want to change them a bit. As a rule of thumb avoid multiple name that start with the same letter. Next read the names ALOUD, to check if any of them sound the same or require pronunciation that requires a double-jointed jaw and the tongue of an ant-eater.
Is your amazing character name 14 syllables long or comprised of multiple titles? Use it sparingly and make sure you have a short-hand version for regular usage if the character is going to appear regularly. Naturally if you’re writing first person that name gets boiled down to I and me pretty regularly, so that point of view is far more forgiving of a complex name for your protagonist.
What’s in a name?
Building an alternate reality Venice, you probably want Venetian, Florentine, and Italian names. If your scene is set on a gondola and all your characters carry Slavic names like Vladimir or Tatiana, anyone with knowledge of the cultures is going to experience dissonance that may ruin suspension of disbelief.
If you are writing a modern piece, or one set in the future, you’ve got a lot more freedom. You might want to look at your world plan, for example if China is the dominant power then a large portion of your characters should have Chinese names. Your piece is set in modern day Korea? Then most of your characters should have one of the big family names (see http://koreanslate.com/top-10-korean-family-names-in-south-korea.html & http://en.wikipedia.org/wiki/List_of_South_Korean_surnames_by_prevalence).
When hunting for good character names have a look at baby names by country of origin and meaning, or old historic documents from the area you’re interested in. In short DYR (Do Your Research) and avoid sinking a great story with poorly thought out names.
Additional link for names http://www.writing-world.com/links/names.shtml