| Thundar the Accountant |
I like to build a medieval tone in my world, too.
Social standing, as someone else noted, matters quite a bit. Deference is given by those below and expected by those above. For example, the player characters in my world acquired their first horses, and in doing so, receive a tremendous amount of respect from commoners now. Good clothes, jewelry and armor also add to their respectability. Their social betters treat them more courteously as well.
Superstition and ignorance are important social mindsets. Most of the action in my game takes place in a long standing elven kingdom, but the elves of this place rarely leave the cozy lands of the ten cities of the realm. Who wants to go mucking in the woods? It's dangerous, and uncomfortable. Players are genuinely confused, and somewhat amused by the elve's attitude, but I think it adds to the feeling of the world considerably.
I put the dampers on wizardry for the public good, such things are magic lightposts and public illusions for entertainment -- basically magic civic improvements that mimic our modern life. I make it a point to stress that everything is made by hand from stone and wood, leather or plant.
I also use medieval prints and artwork (google search) in materials I give to the players -- maps, writeups, diagrams. Used consistently, it gives my world a certain look. Also, when I write descriptions, I emphasize what I imagine the medieval world would look like -- a lot mud and horse flop.