It is vitally important to keep your out-of-game knowledge separate from your in-character knowledge, and to act naturally when discussing stuff your character shouldn't really know anything about.

Some players learn this quickly. Others... don't.

Transcript

Obi-Wan: You see, you can do it.
Han: I call it luck.
Han: Great rolling!
GM: You're coming up to... Naboo.
Han: Right, uh, good.
Chewbacca: You know, one of us should probably be at the controls at least most of the time.
R2-D2: {softly} Especially given our recent record with unattended cockpits.
Han: Ah, yeah. Let's go. Because I am absolutely the captain of the Malteser Falcon. And you are my daring assistant.
Chewbacca: Quite so, my dear captain.
Han: I am sure that we will have many fun adventures on the surface of the planet Naboo with our friend Jar Jar, who will surely greet us there upon arrival.
{beat}
GM: You know, I can never tell when you're being sarcastic.
Han: Good roleplaying, huh?
R2-D2: Now that's sarcasm.