Instead of having the large, classic gods, use small gods that take the frm of huge beasts, terrain features, or monuments. Clerics can only cast spells if they're in a certain mile raidus of the small god.
Use the barter system. Eliminate currency. This will allow for more role playing interaction and the use of CHA based skills more oftern.
Have the player characters all be of aquatic races. This makes for a great ocean based campaign.
Travel. Eliminate teleport, whispering wind and such. The easiest way to travel from one village to the next is on horseback. Messages are delivered by the Pony Express.
Ethereal. Make most magic connected to the ethereal plane. Invisibility won't make you invisible it merely makes you ethereal.
Status. Introduce the Reputation statistic from Dragon Magazine. Rep=Lvl+Chr bonus+Bluff+Diplomacy+Intimidate.
Honor. Use the Reputation statistic from above but substitute Bluff, Diplomacy and Intimidate for more (in your world) honorable skills. Such as Ride, Profession (Painting) and Perform (Poet).
Frostmarrow said:* Ethereal. Make most magic connected to the ethereal plane. Invisibility won't make you invisible it merely makes you ethereal.
WSmith said:
Another is using non-standard structures in non-standard evironments. For example, when most people think of pyramids, they right away think of the desert. How about placing them in the snowbound north? Structurally, they are perfect to allow the snow to slide off.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.