Random Encounters

Go deep enough for meaning and wide enough to be surprised and inspired.
Determine number appearing, leaders, special items, and activity in advance.
Determine surprise and distance during play.
Don't improvise encounters with monsters you've never used before - they deserve a fantastic, memorable encounter demonstrating how they're unique.
The world can be generated/discovered during play, but the players must believe it exists prior to perceiving it, and what they discover must remain established. Locations shouldn't move.