I try to think logically for them. Not TOO logically; a lot about them doesn't make any sense. Plus, y'know... magic, dragons, fantasy? Still, some things I try to focus on:
- Longevity and power: dragons are like a fine wine; they only get better with age. I think dragons, like elves and other long-lived races should tend to look past right now. Some however I feel should be obsessed with history since they hoard stuff
- The ultimate hoarders: dragons, really impressive dragons should have tonnage. I'm not just talking money and magic swords. Consider if a human being with a tendency toward... collecting, had centuries ahead of them. Having an entire cave dedicated SOLELY to baseball cards wouldn't be out of the question
- Mating: let's face it; dragons get around. Half-dragons, sorcerers, younger true dragons, potentially kobolds, and then all the lesser dragons like drakes, tatzlwyrms and pseudodragons. These things have to come from SOMEWHERE. If you decide they ARE related to either Chromatic or Metallic dragons then unless they're experts at genetic engineering these creatures are finding SOME way to get it on with anything that isn't food at the moment.
All of this usually leads me to the inevitable conclusion that dragons have TONS of minions, spies and allies. Even the good ones. Think about it: even an egotistical black dragon heady with it's own power has got to admit that it's mortal and can be killed by a band of adventurers. Therefore, looking ahead to the future it's likely got some kind of survival plan and a way to dominate its environment through progeny, controlled reptiles, and piles of stuff in order to insulate itself from potential enemies.
I like to run dragons, even those of lesser intelligence, as schemers and clever manipulators. Take a simple, white dragon. It's not a chess-playing mastermind but it knows that survival is a long-term game and it's environment is resource-constrained. It mates with every herd and sentient creature it can; gross as that sounds it ensures that its own draconic virility affects its offspring and increases long-term replenishment of the altered species it creates. It might then pick out some weaker members of its own offspring; a mutant half-dragon elk or perhaps a sorcerous member of a barbarian tribe. If successful the white dragon can use these beings to bolster its own survival, all the while using it's own superior power, hoard and experience to keep the offspring in check and ultimately slay them to start over with a new batch.
Finally a note on hoards. Other posters on the boards have written about this but I think it's worth repeating: hoards don't need to JUST be money. You draconic villains and allies might hoard other physical things, like snow globes or shipwrecks. They may also hoard information: imagine a dragon with access to the internet. Its name would be Wikipedia. Still others might hoard minions. No two dragons should ever be truly identical.