I think as important as teaching game mechanics is it's equally important to teach newbies the culture of their new realm.
Players should invite newbies to join their guilds and religions. They should tell them some gossip about other nobles maybe try and get them on their side for ongoing feudes. They should speak with pride about their realm's history. They should explain why they're at war and why the enemy is the most hated foe imaginable. Or conversely they should explain why they're at peace when they should instead be waging war with their hated former foe.
Seasoned political players should see new nobles as soft malleable clay they can mold into something useful. Manipulation and indoctrination should start at day one.
