Being able to write creatively takes talent. Being able to sit down and write a full-length manuscript takes discipline. Being able to self-publish takes both of these and determination. If you have all of these three traits, then you are taking that first step on the long road of getting your book self-published.
I, myself, am currently looking into trying this. I have never published a book (be it self or through a publishing house) in my life, but while I tend to do things by the seat of my pants, this is something that simply cannot be done when choosing this route. Like with any serious venture, this takes research, hard work, time and commitment as well as a financial ability to carry it all out.
If you're going to be writing and publishing your first book, there are some things to consider. Depending on your books genre (be it fantasy, science fiction, historical fiction or a type of nonfiction such as reference materials), you need to know how to pick the right publisher as that each company only takes in specific genres. If you have a mixed one, such as a combination fantasy or sci-fi, your choices are limited further.
Then you must take into account that publishing houses tend to be wary of first-time, agentless authors. There is a risk involved as that you are not established and they don't have any idea as to whether your book will be you and them money. As for getting an agent, it's also tricky to work this. It's hard to get into a publishing house without an agent and it's hard to get an agent if you're unestablished with a publishing house. It's a classic catch-22.
Also there is the profits. If your book is successful and you do make it, the publishing house takes a substantial cut for their fees. So if your book sells for $15 a copy and you sell 1,000 copies, you may only get $250 after their fees, whereas if you self-publish for the same price per copy, selling 1,000 copies, you could get about $8,000.
However, self-publishing is not without its financial drawbacks as well. Since you are doing this entirely on your own, you are responsible for not only writing the book, but for editing, design (front and back covers plus any interior design), formatting, printing, promoting and getting your book out to businesses. Each one takes a focussed and concentrated effort and absolutely nothing can be skipped.
There is some help though. You can hire freelancers to assist you. There are ghostwriters, freelance editors and graphic designers. Bear in mind though that hiring any of them will add to your bills. If you do intend to hire professionals, do research on them. Shop around, check their portfolios and references before making a decision.
One site that can assist with some of these aspects is known as Fictionpress.com. Here, you can write full-length stories to your heart's content. There is even a forum where, after clicking to locate the appropriate section based on genre, you can write up a description of one or all of your story's characters and then role-play them out to get a feel for them and work out their personalities. Even if you have no intention of posting a story there, it's still an excellent site to flesh out a story. But if you DO decide to post there and intend to eventually publish your story, I seriously recommend copyrighting your work first to prevent plagiarism.
Even if your work is nonfiction, it's still worth checking out as that there is a section for nonfiction writers. Perhaps you may even find other authors that are working on the same or a similar topic and you can all bounce things off one another such as great research areas, tips and other information.
There are some pros and cons to both self-publishing and going through a publisher's house. It's a personal decision and whichever you choose, I wish you best of luck and look forward to seeing fresh faces on the shelves.