CKII roleplaying tips for (relative) newbies?

So I'm trying to do a world conquest. I wasn't planning on doing one, but I've never done one before, and judging from my current size, I'm starting to think it may actually be feasible before the end date.

So once I finish that, I'm planning on starting a game with an emphasis on roleplaying, rather than conquering as much as possible. But I'm not really sure how to go about doing it, in the context of CKII. So what are some good roleplaying tips specific to CKII? I've roleplayed before, mostly tabletop, but also some on forums.