Even after writing for so many, many years I am still learning what does and does not work for me.
Waking up in the middle of the night with an idea so powerful it's transcended my subconscious mind and I have to scribble it down somewhere, for example, works very well. An idea that starts slowly but keeps creeping back into my head every time I hear the same song also works well.
What did not work well recently was starting with a theme for a short story collection and writing towards it. I was writing profusely - story after story was flowing through my fountain pen. But then... I stopped to read them, and I realised - totally aghast - that they were the most mundane and insipid stories I've written for a long time.... if ever!
So, lesson learnt: write with passion, write a story that can't not be told, write every sentence as though it is the only sentence that matters.... and if after that the stories feel like they belong together, put them together. Ah, that's better.