If you don't care about science enough to be interested in it on its own, you shouldn't try to write hard science fiction. You can write like Ray Bradbury and Harlan Ellison as much as you want.

Science fiction is the very literature of change.

A good science fiction story should be able to predict not the automobile but the traffic jam.

That's really what SF is all about, you know: the big reality that pervades the real world we live in: the reality of change. Science fiction is the very literature of change. In fact, it is the only such literature we have.

On this day I want to tell you about, which will be about a thousand years from now, there were a boy, a girl and a love story.

For someone to be taken seriously it was valuable to have the appearance of someone who deserved to be taken seriously.

The future depicted in a good SF story ought to be in fact possible, or at least plausible. That means that the writer should be able to convince the reader (and himself) that the wonders he is describing really can come true... and that gets tricky when you take a good, hard look at the world around you.