I get a concept and jot down a few notes or a scene.
I break out a yellow legal pad and start what I call the free-ballin' phase where I just throw down everything that comes to mind about the idea. This usually results in new characters, bits of dialogue, plot tangents, sub-text, characterizations and world building notes. Most of it is non-sequential and some of it never makes it into the final edition.
Out of this word hash, I pull my main characters and produce a story arc. I decide (loosely at this point) if the story looks like a short, a novel, would be better seved as a script or if it would be better as a serial.
I do a basic outline in three parts, beginning, middle and end and that outline is filled in, deconstructed and reconstructed many times from this point until I type "The End."
Once I have that, I concentrate on character bios, world building and start finding the "voice" of those characters and how it's shaped by the world I've built for them to live in.
By this point, the story arc and outline have evolved to the point that I start the actual writing process. Please note that an outline is kind of like the "Rules of Piracy" set down by Henry Morgan (ya'ar). It's more of a guideline, really. NEVER let the outline stop you from exploring a tasty tangent. It's there to provide structure, a set of bones to flesh out...not as a Holy Writ delivered from on high.
Once there's a rough draft and it's gone through spellcheck three times, then the dreaded red highlighter comes out. What works, what doesn't, what rocks, what drags its little feet, did I make the characters do anything against their nature, did I screw up the continuity or voice?
Rewrite
Give it to my mate (Obersturmbanfuhrer of the Grammar Nazi's) and rewrite again. Listen to several lectures on proper use of the comma and ellipses. Rewrite again.
At this point, I'll either have another set of eyes give it a look or I'll publish and wait for someone to point out a typo or other goof that managed to survive.