This is an idea I am putting up so I can flesh it out. Many other RPG bloggers have said the same thing. Variations on the numbers of goblins, orcs, kobolds, ogres, etc. and their appearance and weapons only go so far to be interesting and avoid a slog.
Now throwing monsters into an odd situation, like a group of orcs with some stuck in quicksand, or kobolds climbing up or down a sheer cliff, can add some interesting spice to an encounter. Do the orcs help their comrades, do they stay and fight, or run away? Why are the kobolds climbing a sheer cliff? Did they find a cave with treasure, or are they fleeing something big and bad?
Encounter Tables don’t have to be just monsters. They can be natural phenomena, landscape features, special locations, etc.
If not an encounter table or tables, these things need to be kept in mind for wilderness, dungeon/underground, and town adventures.
Pits/Traps/Deadfalls -> Monster or Fen or Special
Quicksand/Muck & Mire/etc.
Tangle of Vines/Dense Foliage