I cheated. I wrote a whole book, split it into three, and voila! A trilogy was born. When I started The Colour of Her Magic in 2006 I did not intend for it to be a trilogy. Most of my writing takes the form of standalone novels. By the time I got to the third draft my book was over 180,000 words and I panicked. Nobody was going to publish this. Hadn't I read all those articles about how first novels should be less than 120k words? But what I could do was split it. There are plenty of articles...
How to write a Part Two