Planning Ahead
I tend to do a little mixing in my games. I plan an over-reaching storyline that will run through the entire campaign (I'm partial to epic stuff, myself ), and then use that as a guide line for writting my episodes. As for the individual episodes themselves, I use three types.
1. Story episodes. These are episodes that forward the over-reaching story of the campaign, and often are the majority of episodes in my games.
2. Character episodes. These are episodes that allow individual or a couple of characters have the spotlight. Often, these are used when only a few players can make it to a game, and will sometimes be used in conjuction with Story episodes. The least used of the three.
3. Random episodes. These are episodes that have nothing really to do with the main plot. It's a good idea to sometimes get away from the driving storyline and do something different every once in a while.
Over all, however, I only have the main over-reaching plot outlined, and am one or two episodes ahead of my players. This allows me to be more flexible when my players invariable take a different course than I had expected.
At times like these I am reminded of the immortal words of Socrates, who said "... I drank what?"