Being able to say that you've written a book is impressive. For those with the passion to write, completing their first book, while notable, is probably not as daunting as what to do with the work once it's complete.
Just like most things in life, getting published is part talent, part luck; being in the "write" place at the right time. But also like most things in life, if you really put some research, time, effort and especially hard work into your goals, becoming published can be a reality.
The first thing any writer must do is produce a good quality product. Plain and simple. Before you can even think about having a book (or anything) published, the work should be grammatically correct, make sense and be free of obvious errors. If your manuscript is sloppy, illegible or unsuitable, submitting it to a publisher is a waste of time.
"Who" you know is important too. Writing groups also offer networking, another major part of becoming published. The most popular fictional genres, romance, mystery and sci-fi/fantasy have many, many organizations of aspiring authors that work together, and with published authors, to learn the ropes. Joining one (or more) of these groups as well as attending as many writing conferences and conventions as possible is like a crash-course in novel writing and publishing.
Writing conferences are also key to networking. In addition to gaining insight into the publishing realm, the classes themselves accomplish many things. Learning different ideas and techniques from accomplished writers, sometimes even famous authors, is a wonderful and inspiring asset in building your skill. No matter how good you are, there is always the opportunity to learn something new.
Once you have completed a good, solid manuscript, finding proper representation is also important. While not necessary, having an agent increases your chance of getting published many times over. The library or bookstore is a good place to find resources on agents. The books, Jeff Herman's Insider's Guide to Literary Agents or Writer's Digest's Guide to Literary Agents, as well as the previously mentioned writing groups are good places to start. Most agents and editors don't charge to review work (outside of modest fees) so beware of anyone offering or promising you publishing for upfront fees in the hundreds of dollars.
Many people start writing their first book with just their gift of creativity and a story that's been inside them for years. Honing the work into a quality product, networking and following through and pursuing the right type of representation and publisher will speed the process to getting published.