The answer is dependent on your goals for getting a book published. If you just want your family and friends to have a copy, then consider using a print on demand publisher. If you have a niche market, or give lectures, then self-publishing might be right for you. But when you ask "how do I get a book published?" you mean "how do I get a book published by a commercial royalty paying publisher" then you have some work ahead of you.
You'll need to write a solid query letter, no more than two pages. That letter describes the concept of your book, or if it's fiction, the hook, why you're the person to write it, who would buy the book, and your writing credentials.
Your next challenge is to write a one page synopsis of your book. It's difficult to condense a 90,000 word manuscript down to 400 words and still capture the flavor of the book and the style of your writing, but that's what you have to do.
If you have decided that you need a literary agent then start narrowing down the field. There are several books that contain lists of agents, what they're looking for, and their contact information. Agentquery.com, writersmarket.com, publishersmarketplace.com are three online databases that can help.
When you've found about 20 agents that represent the kind of books you write, send them your query letter, personalized of course, the synopsis and, a self addressed stamped envelope (SASE). It's important that you include the SASE. Many agents won't respond unless the SASE is included. You can fold the envelope in thirds to fit it inside the business envelope.
Mail off your queries and then start the next batch of agents.
Don't be discouraged by rejection, many of the bestselling authors of today started out being rejected quite a few times before they achieved their goal of getting a book published.
Should you follow up with the agents? No. Agents are contacted by hundreds of writers a week. You could include a self addressed postcard in your query letter package that the agent mails back to you. When you receive the postcard you'll know that agent received your query.
"How do I get a book published?" is a question nearly every writer asks. Don't give up, you can get your book published.
