One of the most common pieces of advice for new writers is to "write what you know". I think this was originally intended to encourage authors to put some of their own experience into their stories, to add authenticity. This makes sense, and I have done it myself from time to time. However, the advice seems to have recently evolved into something much more restrictive, i.e. "write only what you know".
I would encourage new writers out there to do the opposite and "write what you don't know", because it's a lot more fun!
Writing, just like reading, should be a form of escapism. I am a schoolteacher by profession, and would balk at the prospect of coming home after a tiring day and writing a story about the demands of teaching.
Through writing, I aim to come out of myself, explore the utterly different and unexpected. I don't want to write about characters like me (no offense to myself!) so I generally have protagonists in my story that are a different gender, race, sexuality, or even species!
I think this works, because when I write what I don't know, less of me leaks out from between the lines, and that's probably a good thing!