Keith Graham has been an author and a fan for decades. He maintains multiple blogs (some of which are devoted to his stories and publications), among which are his resource pages devoted to the writing of science fiction.
There are numerous helpful hints and various tools on offer at CThreepo.com website, but one in particular is useful, informative and timely:
Keith’s Author’s Note spells it out:
Author’s note: These rules are intentionally provocative, and they have generated much discussion and some intense opinions for and against. This is as it should be. They are not all original with me. Rules 6, 8, and 9 have been stated (in different words) by SF editors for years, so if you write and submit stories, you may have been reminded of them in rejection letters.
As noted, you may agree or disagree, but wherever you come down, they certainly are something to think about.