Over on Facebook, Samuel R. Delany, answering a question in a post, offered the best and most succinct writing advice anyone has ever codified. Here, in its entirety, it is:
Writing advice: Read and reread. Think of a story you have never read but wish you had; then write it as carefully as you can. Finish it, and send it around till it's published.
The third sentence, as Chip noted at the time, was a condensation of advice that Robert A. Heinlein offered. So what you have above is the combined wisdom of two of the greatest careers science fiction has ever seen.
I could unpack that brief paragraph at enormous length. But, honestly, there's no need. You read it and you understood it. Now you only have to live it.
Above: The photo by James Hamilton was lifted from The Nation, where it illustrated a typically thoughtful and enlightened interview with Chip. You can find it here.