What
@Riku says.
Me, I just talk "shit" i guess. Whatever comes to mind, I found out how I wanted my Vlad to be a long time ago. But since then I have just developed the rp together with the players and people I have been around.
But in the bottom I just have decided to be a confused Russian bad ass, that have some hidden soft spots inside. He also think he knows how to run a perfect world, with a lot of fucked up reasons on how that should be done.
Everything else is just what comes to mind when I stumble upon people. I never plan shit, couse then I feel "pressured" to do it right.
RP for me need to be fun, and if I try to plan it and follow to many instructions, I lose my way out of it, or it just comes out as crap.
So my tip would be, get comfy with the character you have created. Find out what he is, what he have done, and try work around that.
When you are in situations you are speechless, well I usually say im speechless
If you cant say anything, its no reason to force it.
And after a while it becomes natural I guess.
That's how I see it, dont know if it's to any help. But that helped me alot