Me, with stories, I make two documents normally. One's the story itself, the other is a notes document where I pour in every idea and every character I can come up with and I combine and make connections and whatever I can, and then I work on the story itself whilst I make even more ideas. That's how I mostly do it as I'm not good at making huge 2-inch binder's full of papers and such. I just make a big paper with notes and scribbles first. It helps me most.

I used to just sit down and start writing.

Then, I'd hit a terrible writer's block and goodbye, story.

Nowadays, I sit down and start writing the main points of the story. Once I have all of them, I start the actual writing.

I still hit writer's block more than I wish I did, but it's less than before and at least my stories make a lot more sense, so...

Writing is something that I do because not having any skill as an artist I find that I can paint with words instead.  When I was going through transition writing was my safety valve and later when I was working as a social worker writing again became my safety valve as a means to survive the pressures of the job. 
Some stories I've written have burst into being fully formed inside my head and it's been all I could do to write them down fast enough before some distraction stole them away.  Other stories have grown more slowly and are a part of my thoughts for several months.  Planning a story has never worked for me.  Somehow a story seeds in my head and then I follow it as it takes shape.  Characters in my stories seem to grow and become very real individuals.  There have been times when I made the mistake of trying to write a character as doing something that's foreign to their personality and find that it can't be done as if the character themselves is pushing against me.  Writing can be emotionally tough as once when a character in one of my stories died I found myself in tears as if a real person I'd known very well had died.  Worse still when I reviewed her death with the thought that perhaps she didn't need to die afterall I found there was no way to avoid her dying.  Stories and their characters have a life thread of their own that I've found I have to respect or else it's pointless trying to take up a pen (or keyboard) and write them down.