This is an excellent question, and one that I often receive. I think people find it surprising that an idiot like me could squirt out a book, given my dim-witted appearance and lack of useful ideas. I get it. And, though piles of books have been written and published on Writing Process and Getting Published, the answer is deceptively simple: just start writing.
Pay no mind to what the writing will be, or where it will be published, or whether people will even enjoy it. That’s called future-tripping, and it fucks people up. Find a notebook and a pen and get the words out of your head and onto the page. Trust the page, and trust in the flow of words from your shoulder to your arm to your hand (or, if you really suck at penmanship, hands). The page is an ideal confidant.
What lands on the page becomes your first draft. My writing teacher, Nancy Beckett, describes the process of writing first draft as “getting your sled to the bottom of the hill.” Ride the sled until it stops at the bottom, and then get off. (If you need inspiration or a little jump-start, find some writing prompts. These are cues for writers designed to get their minds somewhere productive.)
First draft is almost always a mess. When read aloud, it will most likely leave the audience confused and wanting more information. That’s why it’s important to workshop your material with others. A well-structured workshop enables the writer to solicit critical feedback representing the voice of the reader. It gives you invaluable insight into what works — and what doesn’t yet work — in your first draft.
After hearing from the readers, you can decide whether to indulge their curiosities and suggestions in a subsequent draft. And then another draft. And then another.
After a few drafts, start pitching your piece. Check out the HOW TO PITCH section on mediabistro.com. They provide a lot of good information about how to pitch specific outlets.
Happy writing! And re-writing!