Things No One Tells You About Writing a Novel
1. It doesn't matter if you get a world away from yourself - you will always be writing about yourself. This makes writing sound like a rather egotistical affair. It certainly sounds self-indulgent, to say the least. Nevertheless, when people tell you to "write what you know" they are unconsciously tapping into this thought - because your experience is all you know! Every single character will reflect you in some weird way. If you become eloquent when you're being nasty, chances are that a couple of your characters will too. Perhaps even your villain. If you can't stand a particular food or have never heard the turn of phrase "Bob's your uncle", you probably won't be including those things in your writing. Additionally, if you have never worked in an accounting or a law firm, you'll either need to expand your personal knowledge, write vaguely about such things, or not write about them at all.
2. Your experiences influence you more than you realize. There may be things you haven't thought about for years that somehow creep into your writing anyway. The way you felt about your immediate family growing up. A bullying experience that scarred you more deeply than you realize. A near crash on the road that still gives you paranoia, meaning you climaxed your latest book with a major accident in which one of your characters died. No matter how hard we try to be original, there will always be a "sameness" about what we write, because there are particular experiences and events that have shaped us and made us what we are. These same experiences and events become part of the fabric of your work. Which is why...
3. You must keep experiencing and growing as a person to be a good writer. This is difficult for most writers to hear, as we are mainly introverts and don't like to go out of our way to have human interactions. However, if you spend all day at home and interact with nobody, your characters won't be realistic. If you don't give yourself the opportunity to go on an outing and notice beauty around you, you won't be very good at describing things, and it will be difficult to become a rich world-builder. If you refuse to read, read only the same genre, or watch the same television programs night after night without enough variation, your work will be dull and un-inventive and risk falling prey to every trope you can imagine.
The conclusion to all this naturally is - be the best you can be. Know yourself, embrace all that makes you "you" but don't forget to broaden your experiences and increase your knowledge. Every writer is on a journey.