I didn't read every response here, but I hope you found that you received as many different answers as there were people who responded.
Trial and error. One of the greatest things about writing is that there is no one right way to do it.
I found the method that works best for me this way. I jumped right in and just wrote and wrote and wrote. It wasn't working. I found writing forums and read what others did. I tried a few of their methods and found aspects in several of them that worked for me and combined them into a style and routine of my own.
It helps me tremendously to outline. I love the research I do while planning a story. Outlining helps me keep the big things in line. That said, I'm not obsessive about following my outline perfectly. That's where spontaneity and inspiration come in. Inspiration, I've found, comes after you start writing.
Then, I write my first drafts by hand. I was completely against this in the beginning because my hands would hurt. But, a respected writer on another website convinced me of the benefits of doing this. I can type quickly. Almost as quickly as I think. When you're typing that quickly, your brain doesn't have time to mull over the original thought, which is usually not the best way to go. By the time a thought has had time to go from your brain to your hand to the paper, your brain has time to mull it over a bit and, most often, your third or fourth version of that thought ends up being the better version. It's made me a better a writer and caused me to edit a lot less. I use my computer to edit and rewrite.
But, again, this is all personal opinion and what works best for me.