Once for an expedition to the Underdark, I created 12 encounters - scripted in the sense of fully stat’d (3.5e, so not so easy to wing it with monsters with character classes) and a story about what was going on.
Then I rolled for Random Encounters periodically, something like a 1 on a d6 every 2 hours when moving, every 4 hours when not moving (I don’t remember exactly what I setup as the intervals).
When I got a 1, I rolled a d12 to see what they ran into/what ran into them. Some very memorable encounters occurred, like when a PC was refilling canteens during an overnight rest and Shadows wandered up from the underground lake. Tough fight with a PC death because the party was caught unready.
Then I rolled for Random Encounters periodically, something like a 1 on a d6 every 2 hours when moving, every 4 hours when not moving (I don’t remember exactly what I setup as the intervals).
When I got a 1, I rolled a d12 to see what they ran into/what ran into them. Some very memorable encounters occurred, like when a PC was refilling canteens during an overnight rest and Shadows wandered up from the underground lake. Tough fight with a PC death because the party was caught unready.