I don't find writing dialog difficult. When I need to write dialog on a character very different from myself, I usually base it on someone I know or a character from a movie or show. I prefer the former, as the latter tends to be one-dimensional. Actual people are deeper.
For example: Meg is quite intelligent, but a bit emotionally awkward around people her age. It would be easy to write Meg as a brainy snob with no social skills, but this would be a tired caricature. Meg is aware she's smarter than most of the people she meets, and this sometimes causes her to overcompensate and act a bit "ditzy" for fear of people thinking she's a snob--this is part of her desire for approval. She is somewhat conflicted about this: on one hand, she hates that she seems ashamed by her intelligence, but on the other she doesn't want to attract too much attention to herself by being the "brainy girl." She also isn't happy about how much more men seen to like her when they think she's less intelligent than she is...but she likes the attention. Physically, she's aware enough of her own appearance to know that men usually find her attractive, but not secure enough to show it off all the time. All of this creates a lot of ice that Meg has to thaw before she can open up to Garrett.
By contrast, Veles Fraise is ancient and diabolical. He is not wantonly cruel, but only because he couldn't be bothered with the suffering of "lesser creatures." He doesn't disapprove of others using these methods, so long as it doesn't complicate his plans. Fraise is patient, but he's been patient for a very, very long time--even by dragon standards. He is so close to seeing his plans come to fruition, coupled with his own looming mortality, that he doesn't respond well to interference. Hidden in Fraise's actions are hints of his insanity. He's not a raving lunatic, but his dialog seems to convey that he's beginning to lose patience...and when he does, it will NOT be pretty.