Read a lot. Read current books in the genre in which you want to write to keep a pulse on what is selling in the marketplace.
Write a lot. Develop your own style and "voice." Write blogs, entertainment reviews or short stories to develop your talent into a marketable skill.
Write stories and topics for which you have a passion. Don't try to copy what's already on the market. Don't follow trends unless you have something unique to bring to the market.
Write an outline detailing the main plot points of your book. Make it as sparse or detailed as you need it to be. Develop your characters, theme and act breaks.
Research your topic thoroughly before you write, using your outline as a guide. Talk to professionals in the fields that apply to your book and read books to support the action or information in your book. Ride along with an emergency response team or interview a senior who fought in a war, for example.
Write every day, whether a paragraph or a page. Use your outline as a road map to get over any writer's block, and commit to a time frame to finish the project.
Take time off between drafts to come back to the project with a fresh eye. Rewrite your first draft with necessary edits.
Ask fellow writers to read your book after a second draft is complete. Get feedback from more than one source to begin your next edit with their notes.