Scifi/fantasy author Ursula K. Leguin said it well: "God knows inventing a universe is a complicated business."
Whether it's a world of Biblical proportions or something more modest for a fantasy novel, worldbuilding is difficult work. Particularly when it comes to naming characters. (Of course, all God had to come up with was "Adam" and "Eve." From that point on, the characters could name themselves.) The recent guest post by author R. R. Brooks pointed out some of the difficulties involved in naming characters.
What makes a good name? The article, "How to Pick Character Names: The 7 Rules for Choosing Names for Fictional Characters," gives some great guidelines. While the author of the article was not focused on fantasy characters, the principles can be carried over to fantasy writing.
There are many other principles shared by writers. One approach is to make the name of a fantasy character similar to an English name. This can help the reader in remembering the name, as long as it isn't something as common as "Tom", "Dick", or "Harry". It also helps the reader imagine how the name is pronounced, although in my own writing, I don't necessarily care how a reader pronounces the name as they read it. Sometimes a name can evoke certain feelings toward the character (best done subtly). A good example might be "Maleficent." Without thinking, we expect a character with such a name is not a "good" person. A bad example might be "Prince Valiant," which is much less subtle. Some of the worst character names I've come across were ones that were simply English words spelled backwards, such as "Osneve Ylnoelcitset Eno" (from a fantasy novel I read as a teenager) or "Tixe Ylno" (a villain in an early Man From U.N.C.L.E. novel).
An author ought to have some system to naming fantasy characters. In my soon-to-be-published fantasy novel, the names of men and women tend to have endings used just for their gender (e.g., "-or" for men, "-is" for women). In early drafts of the novel, I used the suffix "-ius" in naming characters who were supposed to have significant powers of sorcery, healing, or telling the future. That convention was scrapped once I read an article that pointed out using pseudo-Roman names in this fashion was overused and obsolete. Most names of my characters are a single name (no surname), and are usually multisyllabic. Insignificant characters are more likely to have single syllable names. A demon who figures prominently in the story has a very unusual, guttural-sounding name ("Jogaziddarak") because, well, demons are very different from humans. An unusual name is befitting an unusual character. Another character is known as "Longhorn" for two reasons. First, his "true" name is too difficult for most people in the story to pronounce, and second, it makes it easy to remember him because he carries a long horn of an antelope-like animal everywhere he goes.
In some stories, knowing a person's true name gives one a degree of power over that person. Alas, though I know all my characters' names, it doesn't mean I can always control them!