I have found when I'm reading a novel I get mixed up too easily if two similar characters have similar names. For example, best friends named Mike and Mark. So I avoid that in my own writing.
I also decided that relatively insignificant characters shouldn't have significant names. In "Love, Sex, and Understanding the Universe," I changed one character from Alison to Alice for this reason.
Another thing I have done when naming characters is to have a little fun with it. I had a character named Carol, and when I changed Alison to Alice, I decided I should also have a Ted and Bob - as the theme to the movie Bob and Carol and Ted and Alice, was somewhat relevant to my novel. In my second novel I also use all four of those names.
One of my main characters started out as Clara but I changed it to Bonnie because it was useful to the story-line. Bonnie is not her real name and there is significance in several scenes to both her name being Bonnie - a West Indian guitarist singing My Bonnie Lies Over the Ocean on a beach - and the secret behind her real name, which Bonnie is short for.
It can be tempting to have a little fun by giving a character an unusual name, but that can be distracting. I only use unusual names for unusual characters, such as Flash, a bisexual, punker artist who has an orange crew cut. I originally spelled Derek as Derrick just because it seemed more interesting, but then I decided there was no good reason for it to be spelled in a more unique manner and this might just needlessly divert the readers attention.
I once changed a very minor character's name because I realized that Jamie is short for James and Jamie's brother was named James but called Jim.
Whatever you do, make sure you're being consistent. For a long time, while developing my second novel, I would interchangeably use, Rosalyn, Rosemary, and Rachel for the same character. In the same book I was also accidentally using both Wicked Wendy and Wicked Wanda for another character. The Find and Replace feature of word programs are great for fixing this kind of problem.
I like it best when the character's name just pops into my head and fits well, as if his or her name was inevitable and somehow obvious. Another one of those moments when you feel like the words you are writing somehow already existed and were just waiting for you to come along and transcribe them.