There are of course exceptions to every rule, he said wryly while contemplating the morning rain, but you could do worse than to follow these.  They’re reproduced in their simplest form here, but follow the link for the full text.

1.  Never open a book with weather.

2.  Avoid prologues.

3.  Never use a verb other than “said” to carry dialogue.

4.  Never use an adverb to modify the verb “said”…

5.  Keep your exclamation points under control.

6.  Never use the words “suddenly” or “all hell broke loose.”

7.  Use regional dialect, patois, sparingly.

8.  Avoid detailed descriptions of characters.

9.  Don’t go into great detail describing places and things.

10.  Try to leave out the part that readers tend to skip.

Leonard’s elaboration of Rule 10 is worth reproducing in its entirety:

A rule that came to mind in 1983. Think of what you skip reading a novel: thick paragraphs of prose you can see have too many words in them. What the writer is doing, he’s writing, perpetrating hooptedoodle, perhaps taking another shot at the weather, or has gone into the character’s head, and the reader either knows what the guy’s thinking or doesn’t care. I’ll bet you don’t skip dialogue.

My most important rule is one that sums up the 10.

If it sounds like writing, I rewrite it.

Or, if proper usage gets in the way, it may have to go. I can’t allow what we learned in English composition to disrupt the sound and rhythm of the narrative. It’s my attempt to remain invisible, not distract the reader from the story with obvious writing. (Joseph Conrad said something about words getting in the way of what you want to say.)

If I write in scenes and always from the point of view of a particular character — the one whose view best brings the scene to life — I’m able to concentrate on the voices of the characters telling you who they are and how they feel about what they see and what’s going on, and I’m nowhere in sight.

What Steinbeck did in “Sweet Thursday” was title his chapters as an indication, though obscure, of what they cover. “Whom the Gods Love They Drive Nuts” is one, “Lousy Wednesday” another. The third chapter is titled “Hooptedoodle 1” and the 38th chapter “Hooptedoodle 2” as warnings to the reader, as if Steinbeck is saying: “Here’s where you’ll see me taking flights of fancy with my writing, and it won’t get in the way of the story. Skip them if you want.”

“Sweet Thursday” came out in 1954, when I was just beginning to be published, and I’ve never forgotten that prologue.

Did I read the hooptedoodle chapters? Every word.