Really, it’s the same thing as any other character. I’ve seen well-written [insert anything here] and badly written [insert anything here].
For consideration:
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Where did they come from, where did they go, where did they come from cotton eye joe. In a Generic Human, the reason they became a blacksmith is…some reason. Maybe they like blacksmithing. For dragons, they are born into their flight, and said flight has pre-determined duties. A green dragon that doesn’t know anything about nature/druid magic/etc needs to be thoroughly explained as to how that happened.
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How old are they. In humans, it’s perfectly feasible for the 20 year old warrior to go fight bandits. It’s also still fairly feasible for the 40 year old warrior to go fight bandits (maybe, depending on how far you want to take how WoW treats character progression and character power). There are things that do or don’t make sense given the background. The considerations here are akin to what you need to think about when making a character who’s a mage that’s 20, 40, 100, 300, 3000+ years old. If you choose to go the four digit age or even three digit age route, things need more explaining. A thousand year old archmage can warp narrative just because of how much individual oomph and other utility they have…But they also might not have that oomph and there needs to be a reason why, or why their effectiveness is limited.
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Where did they come from, round two. This is sort of the ‘be aware of significant events surrounding your character’s place of origin’. Characters born in Stormwind should know the history of the city and, based on their age, have an explanation as to how they were/are impacted by events they would have experienced. For our good friendo Sab’s brood, they should know what they were doing out there, the struggles associated with it (Outland is rough, dude), and as a writer I would recommend having at least a general idea of their relationship or lack thereof to everyone else in Outland. Have they ever been to Shattrath? Why or why not? What do they think of the Gronn? Are they old enough to have dealt With All That, or is it more of a story to them? What do they think of the netherdrakes?
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With all that in mind, shaped by the prior questions, what are they doing now and how’d they end up doing that? Also, what individual skills do they have and what do they lack. What reason do they have to interact with anyone else. This also determines what social scenarios they’ll be in, which is important because if you’re in a dragon guild, lounging around as a giant lizard is most likely fine. On the flip side, if they picked the Orc visage because of their interactions with Orc tribes and they’re doing Orc Stuff™ at the moment, or they picked a Draenei visage to work in Shattrath, dragoning up the place is probably less socially acceptable.
This also shapes what conflicts they’re facing, and with/against whom. As another poster mentioned, a something-thousand year old dragon dragoning up local bandits doesn’t make for great storytelling, both for your character and for everyone else’s characters who might happen to be along. Figure out what abilities they do/don’t have, what form they take and don’t take at any given time, and why.
Mind, there are a few good reasons for being an older lizard but still taking a visage form and fighting bandits. Cultural exchange, taking the sneaky-crouching-concealed-hidden dragon option instead of the open one, among others. Another good reason is that siege weaponry exists, or mages with giant pointy icicles exist, and being larger makes for a juicy target more often than not.
Maybe the dragon is young enough that their dragon form could carry one person at best, and thus isn’t big enough to be worth sticking with in combat a lot as the target area increase isn’t worth the extra range/mobility/claws in most cases.
I could ramble on about this, but the long and short of it is that there are lots of details that go into it that need to make sense. These things are important not just so you have a well built character for your own benefit, but also so other people can enjoy them as well.
Bonus: One thing I do I find particularly useful for grounding characters who are more ‘out there’ is to figure out their mannerisms and other things I can add to an emote that link to something else. On one of my SWTOR characters, I tried very hard to avoid using any contractions whatsoever, because as a result of trauma they were hyperformal. Some of my dragony characters have specific things they do or don’t do when referring to someone else because, as a result of growing up secluded or [insert background here], they still struggle with humanoid facial recognition. Some are comfortable standing in the middle of a group, others will always stand in such a way that no one is at their back.
Edit for something important: There’ll always be someone who goes “raaaaah you’re doing it wrong rabblerabble grrrrr”. The stigma is not entirely undeserved, but also the mistakes that created it are 100% applicable to any other type of character. The Basic Farmer Joe who shows up and asks the giant several times their size if they want to roll to figure out who wins the arm wrestle is the same as the elven/human/whatever archmage/druid/whatever is the same as the [insert impolite RP practice here][insert race/class/archetype of choice]. Just be genuine, put in effort, and block anyone who isn’t doing the same.