1. Avoid names that draw from overplayed concepts, like "Death," "Rose," or "Night."
Experienced roleplayers often groan when they see a new Death Knight waltz into the local tavern rocking out the name "Deathnightrose." Of course, the player of Deathnightrose might be the most skillful, entertaining roleplayer ever to grace the World of Warcraft, but most people are expecting bad things right from the start.
There are a lot of interpretations for why the names are bad, but I think the majority of the issues revolve around these names being overplayed. In a world of a thousand roleplayers, "death" is a pretty darn common name. It's just become a generic moniker, and one that very easily gets associated with the worst behavior among roleplayers.
Death, Rose, and Night are my favorite three words to avoid in naming a new character. They aren't the only three, of course. I think that "Moon" and "Luna" have probably been over-used for any Night Elf or druid, and "Sniper" is certainly a tired meme for hunters now.
Examples to words avoid include: Death, night, rose, grave, blood, dark, evil, and raven.
2. If you're going descriptive, aim for subtlety.
It's tempting to name a dwarf character "Ironbeard" and "Grayhair." It's a fairly realistic name for dwarves. Ironbeard is certainly a name rooted in the genre of the game. It blends right in with the Wildhammers and Bronzebeards. But my favorite dwarf name I've seen was actually "Calloused."
The name was a reference to the character's hands. The dwarf was a warrior and a blacksmith, and his roleplay featured the character's hard work and well-calloused hands. The name had implications about the dwarf's stoic behavior, also, just by virtue of that name constantly hovering over his head.
Spend some time considering your character's personality traits. Does your character become fascinated by the world's beauty? Or perhaps your gnome's fingers are constantly stained with ink smudges from his work in the royal libraries. Looking for these little touches of character will help provide you some unique inspiration.
Some good examples of descriptive names include: Subtle, Distracted, Harmony, Taunt
3. Make a name which humans can pronounce.
It's fair to hypothesize that a name in the native Draenei language might be unpronounceable by humans. And that might be true in a strict immersion sense. However, it's been my experience that we all think in spoken language. (On some level at least, anyway.) If your fellow roleplayers are unable to pronounce your character's name in real life, you may find them shying away.
I don't think it's very common, but I've definitely seen some verbally undecipherable names. For example, I've caught more than a few characters with names made up entirely of consonants. You can string vowels together fairly well, but you probably still want to keep it fairly straightforward. Combinations like "ae" and "io" are obviously fairly viable, but I would wonder about a name like "Aierst." It's an unfamiliar construction, and many people will trip over it.
4. Lean on consonants for harsh character.
This is probably a preference thing, but I like harsh consonants for my thug characters. "Kogrok" sounds like a big, tough barbarian who's eager to bash people with his club. It just sounds right to my ear. You can then go the other way around, and use a soft, consonant-light name like "Yalla" to represent a graceful, elegant healer.
5. Count your syllables.
Like I said, this is awfully subjective. But when I am creating a regal, noble character, I often look for multiple syllables. "Baron Ted" probably doesn't work as well as "Baron Theodore." While I'm sure there are numerous examples of famous leaders with single syllables, it's still a general trend in my mind.
6. Avoid homage names.
When Wrath of the Lich King first hit the shelves, there was a small army of "Arthas" names hitting the servers. I think when the A-Team rolls through the theatres, we'll probably see a few Hannibals and Murdocks rocking out the servers. Every time G.R.R. Martin releases a new book, Starks, John Snows, and Eddards rear their head in Goldshire.
I prefer to think of these names as homage names, not "rip offs." I don't think people who are huge enough fans of other works are really trying to be annoying. Instead, they're paying deep respects to the subject of their fandom, and this just translates through to WoW.
Unfortunately, when you're naming roleplay characters, using an homage name just broadsides your fellow roleplayers. They won't be thinking about your skillful phrases and deep roleplay. Every time your fellow roleplayers look at your character, they'll simply be thinking about the source of your name. Ditch that baggage, and cling to your original creative work.
Examples from Lore
Deathwing is an obvious exception about not using "Death" in your character names. Of course, Deathwing has the advantage of having been created may years ago, and also being created by the actual game writers. That's a level of street cred that a level 1 Blood Elf cruising around Silvermoon won't be able to recreate. However, those names are pretty rare in WoW's NPCs.
Thrall's name is actually my favorite among WoW NPCs. Obviously, the name is sourced from Thrall's past as a slave to the humans. However, the subtlety gets involved when we look at how Thrall's grown since those humble origins. He's now a Thrall to his own leadership and his own people, constantly struggling to promote the Horde's goals. It's a beautiful, poetic use of the word, and I've never stopped being impressed.
Kor'kron isn't the name of a specific character, of course. The Kor'kron are the elite guards of the Horde, and every use of them in game clearly involves some kicking of butts. The name, therefore, is incredibly harsh on your tongue. It sounds like a guttural exclamation, which works very well for the Horde's warriors.
Sartharion -- along with all the other dragons -- is elegant proof that many syllables can describe a regal, noble character. Every dragon has a long, beautiful name. (The shortest dragon names I can think of are Malygos and Eregos.)
Finally, don't be afraid to ditch a name if it's not working for you. Hopefully, you'll know whether a name is appropriate within the first ten levels of a character. That way, you don't miss out on much by deleting the character. However, if it's not until level 80 before you get tired of a character's name, you have the option to go for a paid name change.