This must be the most asked question of any author by friends, family and almost everyone else, but do any of us really know?
I am lucky enough to hear voices first and the plot comes later - each one of my novels started with either the hero or heroine talking to me about either a problem they were having, an argument with someone or worrying that they'd made the wrong decision about something. I then listened - hard!
Very soon, I have a premise forming and then I start the nightmare job of writing the five or six page synopsis - if I can give any aspiring author some advice, it's write your synopsis BEFORE your novel, not after. It gives you a referral point to come back to if you find yourself floundering a third or even half the way through the writing the book. It will act as a kickstart or give you a new idea and where to take it. Remember - this is little more than a guide at this stage, you can still write the book as you want it, change it and play with it.
I did and now I've written six full-length novels which I am very proud of!
If you change and rewrite the synopsis as you write the novel, at the end of it you will have a fully functioning synopsis, ready to submit to publishers or agents without having to struggle to come up with the synopsis after the hard work of writing the book - it's already done and ready to go, perfect!
Right, I'm off to start writing the synopsis for book number 8 - bit of an issue seeing as I am working on novel number 7 right now. But this damn hero will not stop talking so I'd better write down what he has to say!