#3. Know what you are writing about.
For example: FACT – a .38 revolver does not have a safety. Yet I just read a best seller where the character ‘couldn’t get the safety off on his .38 revolver in time.’
If you are going to write about guns then Learn About Guns! Go handle one, take a shooting course, go ask someone at a gun store, etc. Just as if you are going to write about sex you should know how to do it! If you are going to write about cars that let’s hope you know how to drive. Silly? Yet authors routinely write really dumb things about stuff they are not familiar with: medical procedures, forensics, and the military.
Another example in a well reviewed novel: ‘Major Thompson steered the ship to avoid a rock.’ Guess what? The Navy does not have Majors or Colonels! A quick check on Wikipedia would have revealed that instantly.
What happened to research? Just because so-called journalists don’t bother to research any ‘facts’ anymore and get away with it doesn’t mean you are free to do so, at least have pity on your more experienced and intelligent readers and check your facts before you write them.