1. Choose names for members of a culture that follow a cultural thread.
Names don’t have to be so similar that they’re indistinct, or rhyme, or all have the same vowel-consonant patterns. But in most successful science fiction or fantasy, names from a given culture have at least something in common.
Think about the ways you can tell a Spanish name from a Russian name from a Korean name, for instance.
Now think about how you can tell a Vulcan name from a Klingon name. You’d know just from the name what kind of creature you’d be expecting to meet, wouldn’t you?
2. Choose distinct names.
As a general rule of thumb, two characters in a book shouldn’t have the same first name unless there’s a specific plot-related reason for them to do so. The same goes for names that sound or look similar. Don’t create that confusion for your readers unless you have a reason to. You’ll be throwing a lot of names at your readers at once, most likely: characters, places, objects and concepts. They’ll be trying to integrate and remember all of these names while they’re trying to follow your story and get the context of the world you’ve created, all at the same time. Don’t confuse them by making them keep ‘Jazon’ and ‘Jaxom’ straight in their heads.
3. Don’t make your job more difficult than you have to.
The more complicated a name is (or the more apostrophes it has in it) the greater your chances are to screw it up. Be aware of complicated strings of vowels or consonants, doubled consonants, and the dreaded apostrophe. Names can and do drift and change over the course of writing a novel. The more complicated your naming scheme is, the more likely it is that you will slip. Apostrophes present complications all their own. Don’t even get me started on what a joy it is to go through and fix four hundred pages of inconsistent straight- and smart-quotes.
4. Don’t make your readers’ job more difficult than you have to.
If your readers can’t pronounce your characters’ names… they won’t. This will not only inhibit them from forming an emotional connection with your characters or keeping them distinct as they read, but it will inhibit them from talking about your book with others, too.
If your readers can’t spell your characters’ names, they won’t. If you’re lucky, they’ll find some abbreviation or nickname for the characters, and if you’re very lucky, they won’t be derogatory. If you’re not so lucky, they simply won’t write about them (or write reviews, or discuss them online and advertise your book through the grapevine) at all.