In accordance with the post-a-day challenge by SunderedWorldDM, whose dreams bore the Orbseeker and whose deeds send the world shuddering.
Various editions of D&D have tried to give you a random encounter table by biome, with one for a generic savannah, one for a forest, etc. This approach has its problems, but is better than nothing when you're designing in absence of a more specific context. But there are some easy ways to improve upon the formula:
- Generally, encountering most animals is boring even though animals are great. I use animal sightings for flavor when the party doesn't have a real encounter. The exception is for animals that engage in some way. Imagine you've never heard of a rattlesnake, and your thief is travelling through the long grass when they hear a rattling sound. What do they do? We are inured to many of the tricks of real animals, but introducing fictional mundane animals with their own strategies and tools can keep things interesting.
- As a corollary, make sure players encounter minor red herrings. If you're planning to have leeches in murky water on the second level of the dungeon, include murky water elsewhere in the region.
- Put people on the encounter table somewhere. Let us see how the environment has changed the way that they live, even when you don't otherwise have a fleshed-out society for them. When in doubt, have them hunting or fleeing something else on the encounter table.
- In settings where this is appropriate, include some divine influence. Fantasy world with tutelary deities often claim to have divinity touching all parts of mortal life. There's no better way to show that than to have the Burning Lions of Sliep-Acc watching you from a distance and tearing apart any thieves they see. Also a good way to bring in the cool apex predators we got rid of because encountering them is boring.
- For the love of all that is good, let random encounters spiral out of control. Put "5 room dungeon" on the table. Put "someone vows to serve a PC in exchange for X" on the table. Put "a messenger delivering the most important imaginable message to a PC" on the table. Let overland travel create plot.