My personal answer is: that depends
For longer fics, I always draw up at least a basic story board and profiles for the main characters. After I'm done with the basics of the profiles, I work out the exact propositions for my characters so they fit with the main plot, before going into the details. One thing I've learned in the process is to not let my creativity be hindered by the story board. When I've got a flow, but I'm not sure if where the scene's going fits the plot, I still keep writing till it runs dry. Sometimes it's exactly what I needed there, other times I cut it out and file it for later use. Sometimes I even give the whole story setup a work over so it fits in. It's still a bit tedious, but also rewarding, especially in those moments of bliss when you look at a twenty page chapter that really propells the story and is catching and funny, and you ask yourself: 'was that really me who just wrote that brilliant piece down in little under two hours?'
I'm not as straight when writing short fictions, but I've noticed that though I don't consider the "technically written" stories to be my best pieces, those nevertheless are the ones that win contests or get published.
From time to time, I've got a story in my mind that tickles my fingers so much I just have to bring it to paper without consideration for the plausibility of the plot or character development, but I've started to always put them into the folder for 'ideas to incorporate somewhere else' and let them rest a few weeks before looking at them again. They tend to need a lot of finishing![]()