The advice would be the same for any kind of fiction. Keep writing, and keep sending things out, not to friends and relatives, but to people who have the power to buy. A lot of additional, useful tips could be added, but this is fundamental.

Research is of considerable importance in certain fields, such as science and history.

I suspect that writer's block afflicts mainly people who have some stable and ample source of income outside of writing. So far it hasn't been a problem.

I wouldn't like to just do one story or one type of stories all the time.

I guess if one set of my books was selling like Stephen King's, and the other wasn't selling at all, editors would want me to do the ones that sold like Stephen King's. But they seem to be willing to let me pick what I want to do next.

I finally decided one day, reading science fiction magazines of the time, I could do at least as well as some of these people are doing. So I finally made a serious effort.

The comments I most appreciate come from ordinary readers who've happened on one of my books at some time of stress in their lives, and who actually credit the book with helping them through a bad time. It's happened a few times in forty years.