I guess I'm a Planner, more than anything else... well, procrastinator, if we're gonna be precise :D
I always like to bat around the prompt or bunny by myself, see what comes of it first. Once I've got the basic idea settled and the main plot line organised, I'll start writing down the ideas and some kind of loose plan as things come to me.
It generally ends up a short, one line at a time, list of events;
Run across beach
... and so on, adding things in before if necessary to help the story. I will usually have a rough idea of what I want the scene to look like and occasionally expand on these lines if necessary. I'll write more as required to make sure the scene is relatively clear, so I don't forget what I wanted to have in there.
Then, when I'm ready and have done as much of the plot or chapter as I can, I go back and start fleshing out those little lines into sensible prose. I'll almost always have a chat with Shinigamioni, my go-to cheerleader and pom-pom, at some point during the process, cause she will almost always come up with something interesting for me to consider (I can recommend Shinigamioni, very very highly, cos she's awesome!).
Having a cheerleader is an invaluable part of my writing process because she's able to look at my plot from the outside and see any potential pit-falls or suggest ideas that may be good.
And that's my Planning process.
I then sit back, wait until about one to two weeks before the deadline, then panic, stop sleeping, and spend every night, writing till 0200 :D