Okay, I'll weigh in -
"These are rules I’ve picked up along the way to help me remain invisible when I’m writing a book, to help me show rather than tell what’s taking place in the story. If you have a facility for language and imagery and the sound of your voice pleases you, invisibility is not what you are after, and you can skip the rules. Still, you might look them over." So sez Mr Leonard. So, let's look them over... but first I have to ask, who is the judge of your "facility for language and imagery"? And why does that "if the sound of your voice pleases you" sentence have an air condescenscion...? But let's go straight to the rules, assuming my "facility" fails the test:
1. Never open a book with weather.
Sorry, no. I've done it at least twice... when it was appropriate to do so. I will agree that if you have nothing else to say then it's a copout and pure padding- but in both the instances where I used weather, weather fit into the place it was put. Perhaps Mr Leonard just doesn't care for experiencing weather, the way some of us - or some of our characters - do. Sometimes a hot summer is really a hot summer, and sometimes it's setting the stage for a set of circumstances where heat saps energy, frays tempers, and inflames passions to the point of sparking... the rest of your book.
2. Avoid prologues.
Done those, too. WHen necessary. They work in the context in which they were put, in my own books. I will admit to a lot of fantasy novels apparently having prologues for the pure hell of it - but what in blazes is wrong with putting a chunk of backstory which is important to the rest of the book - but takes place too early for it to be incorporated into the book proper - into a prologue which is right up front and allows the reader to GENTLY get up to speed? On the other hand... Mr Leonard writes in a particular genre where prologues are not only unnecessary, they may well slow the pace of the book dramatically. But hey, that's a different thing than a global "avoid prologues" dictum handed down from on high. If they work, use 'em. If they don't, then don't. It's your book, your story, YOU get to decide.
3. Never use a verb other than “said” to carry dialogue.
Actually, that's not a bad rule. Newbie writers trying to be "original" will wind up with manuscripts where people hiss, mutter, shout, ask, whine, growl, snap, whimper, howl, wheedle, even ejaculate (don't laugh, it's somewhat old-fashioned but it's still around) and the reader is left guessing HOW the character will utter something next, not focusing on what that character is actually saying. Add to that other pitfalls, like the fact that you can't actually HISS something with no S's in it... well, you can see where this is headed. "Said" is invisible, for the most part. It leaves people to concentrate on content, not context. Which leads us on to -
4. Never use an adverb to modify the verb “said” . . .
Been there, done that. The REAL rule is "use adverbs sparingly", not don't use them at all. Try this for a trick - take a couple of pages of your dialogue and highlight in neon yellow every qualifying adverb of the word "Said" that you've used. If the page starts looking like it's had a severe attack of jaundice, you're using too many adverbs. If you find one or two yellow streaks per page, you are okay. Really.
5. Keep your exclamation points under control.
Let's just say... they undermine your credibility if used incorrectly. That's how I know that some of my email is actually spam. Anything that tells me to "Update your account!!!!" is unlikely to be genuine. You see what I mean.
6. Never use the words “suddenly” or “all hell broke loose.”
All right - but what it something did happen "suddenly"?... Honestly, it's better to use a cliche sometimes if it actually fits the situation then to tie yourself in linguistic knots (however high your facility with language might be) trying to avoid one. Use your own judgment - or, if you don't trust your own, use the judgment of a beta reader. But you WILL be able to tell when the immortal prose you are penning starts to sound ridiculous with convolutions. At such times, it suddenly feels really GOOD to cut through the verbiage with a sharp editorial knife and restore simplicity and clarity.
7. Use regional dialect, patois, sparingly.
I've read one book where this was a real problem, one that repeatedly jarred me out of the narrative - one of Richard Adams's, where a Geordie (=North of ENgland) fox uttered everything in this thick accent which took me so long to work out that I eventually lost interest in the entire book. I suppose there is also the danger of sounding awfully twee if your characters insist on using the word "Wee" to describe every "lass", and stuff like that. But think of this as a condiment rather than an ingredient of the stew - a little goes a long way - and you should be fine.
8. Avoid detailed descriptions of characters.
I dislike intensely the "she looked in the mirror and her dark eyes stared back at her from a chiselled face with high cheekbones and thin lips, framed with wild dark hair..." passages. How many people do YOU know who look in the mirror and start enumerating their physical characteristics? Just how important is your character's physical appareance is important, it will become a part of the story - descriptions for their own sake are not only boring, they're unnecessary. PARTICULALRLY if you're writing in first-person - YOU try and describe yourself and see how far you get.
9. Don’t go into great detail describing places and things.
Again, this is a thing that works wonderfully well for Mr Leonard's genre. We all know what a street looks like, or a dingy office, or a car. We don't need to have it described. But I... I write fantasy. I write about places that people other than myself have never been. I need to describe these places. Besides, I have this [cough] facility with imagery - and my descriptions are usually both useful and, well, they've been called *lush*. I wrtie immersion. I create worlds. I LIKE doing that. This is not a rule that I can live by.
10. Try to leave out the part that readers tend to skip.
...Uh. Which particular reader? And how the heck would I know what someone else would sklp? Put in what YOU would not skip. That's the best you can do, under the circumstances, not being psychic. The real rule is, you simply cannot expect to please everyone all the time, and if you try you weaken your story, your prose, your voice, and the integrity of your book.
The only rule is, write what you love, write it as well as you can.