I have one writing tip and one writing tip only – what you write and how you write it is entirely up to you (even if it’s bad): Write constantly.
Even if it’s only a 100 words a day, over your lunch break or some other moments of time to yourself, over the space of a year that’s 36,500 words in a year. Double that figure and you have yourself the first draft of a short novel.
Never stop writing. That’s about it, really.
At the moment, it’s the advice I’m taking to plough my way slowly through the first draft of my second novel.