When writing prose/poetry that tells a story, do you have a clear idea in your head and begginnig, middle and end?

Or is it just stream of consciousness flow of ideas.

I'm on a bit of a prose writing thing at the moment and I was wondering if any of you planned out before hand the ideas you wanted and where and when to use them. For me, I usually write without a plan but then, if I really like the piece, I'll refine it and refine it, make it more cohesive and strcutured and the like.

So would anyone recommend planning? This is relevant more to prose than poetry but there are certain poems I think could gain from planning.

Honestly, as I've been attempting prose lately, I do start with an idea. When I write stories in my poetry (which is prosey anyways), I tend to come in with a stanza or a line in my head that I want to use, and then write around that idea. So yes, I usually have a very geneal and vague idea about what I'm doing... but I rarely have more than a single line to go on.
The way i work is that i've first got a concept to work around.
Like for this little comic i'm planning to work on, the concept is it revolves around this dark superhero. He's a trained in martial arts and stuff. He's in this city, the people in the city count on him to save them but he's not the angel the think he is. He's dark. And then it doesn't have a happy ending.

So as you see its really vague, its just a very loose concept. Then i start writing and the story develops as i write.

Same goes with songs/poetry. I've got a concept or i pick up a key sentence like my latest one is "falling apart like autumn leaves". Now i use that sentence to build a concept around it and that'll give me the idea for my song/poem. Another one i've been working around is "she lets you inside of her". Thats a catchy line and i can build a little concept from it. Could be about a person whom you were with, you loved and trusted, she let you into her life but then it was dark in there, it was sinister and you can go on from there with the concept.
Then i use some pain and inspiration to get the flow. Lately i've been using my ex and NIN for that! But well, you get the idea.
And many times while writing songs i come up with chorus parts first then i write some verse bits to go around it or it could be that i write the 2nd verse first... ya know. it doesn't need to be written in the right order.