The most potentially difficult but most fun part of "restocking" my megadungeon is filling back up the rumors table. Since I use a d30 and a 30-rumor table, I have to keep a large number of them on the table at once.
Basically how I do it is to open the Rumors doc file, and systematically go through the table filling in blank spots. Stare until something comes, and then write it down. If I end up with extras, I stick them at the end of the table for next time - they aren't rumors yet, just ghosts of rumors future.
I have a few guidelines I follow.
- Write down every crazy rumor I think of, as I think of them. Whatever pops into my head. I fine-tune them but I don't erase them or agonize over them. I'll need hundreds of the lifetime of the game, so why get picky?
- I don't decide if they are true or false. I don't mark them for accuracy or veracity. They could be true, they could be false; they could be true but lead you astray, they could be false but lead you to a real truth. It's not really up to me to decide ahead of time - play and the players will determine what really turns out to be true.
- Use them to pass along hints and background detail. No one wants to read an essay about the dungeon. But they'll cheerfully put up with history given a rumor or two at a time. It'll all start to fit together organically.
- Add some the players ask for. If they're researching demons, maybe some extra demon rumors come up - after all, people hear you've been talking to Thaddeus the Sage and they know something that ivory tower fool won't tell you. And who knows, they might have a tidbit that helps (even when it's wildly wrong.)
- Have some rumors come with handouts - maps, letters, etc. Do it sparingly, but do it. "Some guy hands you this burned piece of paper he found crammed into his uncle's old "hiking" pack." "You find this half of a map while researching spells." "Someone sketches this symbol for you and says he saw it in a dream." Whatever.
- Feed the player's own ideas back to them. Write down some of the crazy crap they say and forget they said, and have a drunk old man tell them that in town. Especially if their crazy ideas are probably true, or impossibly false ("See, I was right! There is a beholders-only level 4.5 levels down!")
- Use the rumors to occasionally explain puzzle bits, oddness, or strange things the players can't figure out on their own. It makes the dungeon come alive when the players meet the son of the guy behind the Kilroy carvings or who can explain why that arrow mark is on the floor. The occasional rumor that badly messes up stories of what the PCs did too, can be fun. "Some guys must hate doors - they trashed every door on level 1" "Heh, no, we missed a few."
- Make sure to keep a list of the ones they heard, so you don't repeat yourself word for word. Repeating partially is great, though, by accident or on purpose. It reinforces the knowledge gained so far.
And just keep writing them down.