Heh - Been there Rafael!
As a slight threadjack...
Think in growing storyarcs instead of storylines.
What I mean is you have your BBEG with his/her/it's Master Goal, as oppossed to Master Plan.
- In two game years the BBEG will be ruling the city-state of Maktios.
- The BBEG starts from a small base in the Sedgewick Fens.
- The BBEG will stop at nothing to achieve the Master Goal.
So, you start putting together events that the BBEG will try to achieve the goal. During the next two game years, you be sure to drop in scenarios that somehow tie into the BBEG's Master Goal. The PCs determine how they interrupt those events.
Do not make any preconceptions on how they must stop things. Just figure out things that the players may, or may not, become involved with.
Now, do that two more times with different Master Goals for different BBEG's.
Here is the key, let events run themselves. If the PCs aren't picking up any of the story arcs, then make it a little more personal. Maybe they are duped by one of the BBEGs into retrieving a useful item. Maybe the PC's favorite tavern is burned to the ground by the BBEG's cheap labor. Just toss the hooks in front of them with tasty bait and see which hooks get bit.
The advantage to this is that you have other story arcs happening and other events in the game world. Maybe the PCs bite at hooks for two story arcs, that's great! Maybe they abandon one story arc for another, that's fine as well. In between adventures, you can have the PCs hearing about the other story arcs are distant events. They know the world doesn't revolve around them, even though the campaign does.
Verisimilitude. The game world is a dynamic environment and the players get to see exactly how the actions of their PCs are affecting things. BBEG #1 was the guy they shut down when they got really torqued off and hunted him down in his lair when they were 5th level. That guy definitely should not have hired that punk thief to steal the wand of fireballs from the PCs. BBEG #2 is the warlord that just overthrew the tyrant 3 kingdoms over. (Too bad there weren't any adventurers to stop that guy eh?) BBEG #3 is the innocent looking priestess that just asked them to retieve a holy artifact from a vile dragon. OK, she neglected to tell the PCs that the dragon was a bronze dragon and the holy artifact is an Angel Bane morningstar, but you know, these things happen. But over the last few levels she has already asked the PCs to clear out that tomb and return that magical iron crown that was buried there. And then she recognized that the brigands in the hills were in possession of a Staff of Necromancy and hired the PCs to retrieve it so she could safeguard it in her temple. She has been so helpful with cheap, or free, spells. She couldn't possibly be evil, could she?In the meantime, you have begun putting hooks out there for two more story arcs to plan for higher levels and to keep options open to the players. That way, they never feel that they can only do one thing.
You just need to remain a couple of sessions ahead of them as far as planning & prep goes. Maybe even just one session at times. Know where your story arcs are going, but don't know exactly how they have to arrive there. As well, you need to sometimes throw in encounters that have nothing to do with the major story arcs. Verisimilitude. Not everything in the world is happening just because of the three major story arcs.
I once built a fortress for some yuan-ti on top of older ruins. The PCs decided to investigate the ruins below to see if they could sneak into the fortress. They found a bunch of undead, had some encounters they didn't anticipate, learned more about history, found a nifty treasure, caught a terrible disease and still did not find a way into the fortress. They did find out the yuan-ti had sealed the passages from the ruins though. It had nothing to do with the major story arc. But the players all had a sense of satisfaction at what they had achieved, and what they had learned. They got themselves cured and headed back to deal with the real story arc.
In the current campaign I run (in which Macbeth plays), the PCs chose their latest adventure. I had several other options floating out there, but they thought hunting gnolls sounded the most interesting and feasible. Since then, they have found out how ruthless these gnolls are, and I think they hate the gnolls for it. They have also found information about an ancient culture and they are thinking about investigating that in further detail. As well, those other story arcs are still moving. So when they finish this story arc, or leave it, or whatever, they will hear about what else has been happening. Then they can decided if any more folk in the world need their help.
I call it juggling tension points. I create events that will occur, unless tension is applied. The PCs cause tension and then I figure out how story arcs will adjust to that tension. Sometimes, the PCs cause so much tension that they break things. Say they expose the BBEGs plans so others deal with them, or the PCs personally take out the BBEG. Either way, the tension the PCs caused had a result and the story arcs without any tension keep trucking along.
I'll be quiet now. I tend to babble when I begin discussin some of my DM thoughts.
