There appear to be two schools of thought (at least) regarding how much preparation should go into writing fiction. One is the outline - giving yourself a framework in which to write, and knowing what the ending will be before you write a single word of the beginning. This requires more up-front effort, but can make it easier when fleshing out the outline by going from point to point. The more detailed the outline, the more information you know ahead of time that will inform your writing.
Pantsing, on the other hand, is writing by the seat of your pants - thus the name. You don't know what the ending will be before you start writing, and it's possible you don't know what the beginning will be, either. You start with a vague idea of what you'd like to write, maybe a couple of character sketches, and you just start writing and see what happens. You may have a a few plot points that you know you want to work in somehow, but you don't know where or how just yet. This seems to be a popular method of getting through Nanowrimo, and offers the most opportunity for surprise as characters and plot take unexpected turns.
Which way to write depends on the person and the circumstance. I tend to write this blog as a pantsing exercising, coming up with a topic and starting to write until something catches. All I can say is, you guys should be thankful that I can edit this before I post it.
As for my fiction writing, I've found myself becoming more of an outliner in the last few years, and my outlines have become more detailed over time. However, I do still have some pantsing aspects to my writing, and there are certainly things that come up that through my outline out the window. I like the hybrid approach, because it gives my characters room to grow in their own way, while still giving me goal posts to aim for.
What do you think works best for you? Do you prefer to have a detailed map going in, or would you rather wander aimlessly and possibly find some really awesome things you never would have known to look for?