There is a future and it will be different - the sci-fi writer's craft
In one sense, I've been writing since I was six. I always had to tell stories, though. I made my first pro sale in 1993, a short story I'm still proud of, but before that lies thirty years of gradual improvement.
I had produced my first novel at age 16. It was, of course, dreadful. I produced another, a gritty piece of social realism, when I was 20-something, and it was worse, since it lacked colour and a resolution. And a plot, too, because I'd been taught at Uni that a novel with an actual plot was very suspect. It took me years to shed the damfool notions they teach in Lit courses there.
It isn't a conscious decision, what you write. Or not for me, anyway. Inspiration? I know there's a story around somewhere when a question occurs: "What would happen if...?" and the bit represented by the ellipsis is fairly specific. To prompt that question, I have probably heard something, seen something, read something... and it figures that whatever it was must have interested me. Science fiction doesn't necessarily come out of science, though. It comes out of putting fewer constraints, but making them technological ones, on the "if" in that question.
You start doing that when you read science fiction a lot, and I do. Why? Well, because I enjoy it. What I most enjoy about it is this: it supposes that there's a future, and that things won't be the same.
Much of the "realist" literature of the 20th century assumes that there isn't a future, or that nothing really changes. A lot of it makes a point of returning everything to the beginning again. That's a theme that's overdone, if anything is, and to a far greater degree than anything in sf. But science fiction can overdo things, too. The Frankenstein plot, for example. Can we be destroyed by our technology? Interesting question. What if we were? Why, then, the ending to the story would be "Then we all died". Lousy ending. Lousy story. No use writing a story like that.
But, you know, we do all die. Lousy ending, but it's the one we have. So stories are concerned with how we get there, and what we do along the way. The Best is Yet to Be is about that. It came out of a question: "What if there were crew on light-speed starships?" Essentially: how would they get on, given that they live in collapsed time? Who could they relate to? The answer to that question wasn't the story, it was just an answer to a question.
The story only happens when you put people in. People who have to handle the question and the answer, and get on anyway. A person who lives in collapsed time could only relate to one who didn't if the latter were very long-lived. That threw up a huge number of other questions, the answers to which have got to be something different from "Then we all died", not because we don't, but because it's a lousy ending. And off I go, to find them.
If there's anything that informs me about telling stories, it's this: there is a future; it will be different; we have to deal with it with something better than "Then we all died". Well, I have to, anyway.