The first thing to understand about novel writing is that autobiography does not sell. Unless you're an ex-president or otherwise famous, people beyond your family and friends are unlikely to be all that interested in your story, no matter how fascinating you might imagine it to be. After years of experience, publishers have learned that most autobiographies simply don't sell very well.
Still, your novel can actually be adapted from your life's story. You simply need to transform it into a story concept that is interesting. Writing what you know is good advice. But increase the level of conflict and action.. Put your story into a time and place that are out of the ordinary.
And create a plot. There are only a handful of plots that exist. In fact, most can be broken down to what the mythologist Joseph Campbell called "the Hero's Journey" or the monomyth. In his book, The Hero with a Thousand Faces, Campbell writes, "A hero ventures forth from the world of common day into a region of supernatural wonder: fabulous forces are there encountered and a decisive victory is won: the hero comes back from this mysterious adventure with the power to bestow boons on his fellow man." Campbell describes seventeen stages along the way of this myth or story format. If you watch movies or read novels, you'll find that they generally follow this basic pattern that Joseph Campbell noticed. The first Star Wars movie is a very good example of this, since Lucas consciously adapted Campbell's format. But you'll generally find the pattern exists in everything from romance to mysteries to westerns. So study some movies or books and pay attention to the structure. Analyze how the story was told and how the whole thing works. Remember, too, that your primary goal in novel writing is to entertain your audience: make them want to keep turning the pages.
After you've come up with a story idea—usually a "what if" scenario—and after you've plotted the basic structure of the story—then you need to come up with your characters. You'll need conflict, so you'll want good guys and bad guys. They can be conflicted and complicated if you'd like—the more depth the better—but there need to be clearly defined "sides."
Be sparing in your descriptions. Avoid an overuse of adverbs and adjectives (that is, avoid words that end with "ly", such as "really" or "badly" or "lovingly." Let your verbs and nouns do most of the heavy lifting. Keep your sentences active, rather than passive. "Sherman punched Joe in the face." is much more interesting than "Joe was punched." Remember, you're writing a novel, not a bureaucrat's explanation of why he needs funding this year. Passive voice should be used very sparingly.
Begin the story in the middle of the action. Don't begin with just one character—have at least two. Don't begin with the character in bed or taking a shower-- or doing any sort of wool-gathering. Avoid the "information dump" where you think you need to tell the reader everything you imagine they need to know in order to understand the story. Comprehending the story, getting to know the characters should be more like real life. Walk into the room and discover a fight going on: you don't know why they're fighting or who the good guys or bad guys are. As the story unfolds, you'll find out. Don't give it away up front. Keep the reader a bit off-kilter, like your first day on a new job.
Watch your point of view. Decide whether you want to write in first person –that is "I was walking across the street and then I saw her." Or third person, "He was walking across the street when he saw her." And then, once you've decided on a point of view, stick to it. If it is first person, remember that unless you're God, you don't know anything more than you can see or hear around you. If you're writing third person, don't jump from one character to another. Stick to one character's point of view through the entire scene or chapter.
Make certain that the characters are distinguishable from one another. They shouldn't all sound just like you. Imagine you're an actor. You're not playing yourself. If the characters come alive in your mind, become individuals, like your friends, and you recognize them by how they act, what they are interested in, by their mannerisms and quirks, then you've done your job right. You may find, in fact, that the characters actually take on a life of their own and gain a certain amount of autonomy. That is, you realize that given their nature, they must sometimes behave differently from your initial expectation for them back when you first planned the novel.
Finally, you must actually begin to write. Find a time and place to write every day that fits your schedule and then discipline yourself to do it. Never go back and rework any of the pages you wrote until after you have finished writing the entire novel.
If you write even one page a day, after a year you'll have a completed first draft, which will be just the right length for an average novel: about 90,000 words (365 double spaced pages). At that point, you may begin the process of rewriting. Keep rewriting until you are fully satisfied with it. Read it out loud to yourself and listen to it. Does it sound right? If not, fix it. Find a friend who will read it and give you honest feedback. Make more changes. Maybe inflict your creation on multiple friends who you know will tell you what's wrong with it. You don't want pats on the back. You want cold hard reality. Develop a thick skin and don't fall in love with your own words.
Then get a copy of Writer's Market from your library or bookstore and follow the advice there for proper format for your manuscript, for how to write query letters to agents or editors, and use the book to find the agents or editors who might be interested in the sort of book you've created. And as you're shopping that book around, start work on your next novel. Then be persistent—and don't give up!