Indeed, "write like you talk" is not quite the right way to go about it. In my experience that usually leads to a stream-of-consciousness mess.
However, one thing I have found almost universally helps my students is similar: read what you have written OUT LOUD. Is it halting and hard to read? Confusing and obtuse? Then you should probably fix it. There seems to be some magic about actually speaking the words out loud (as opposed to just reading it like normal editing) that helps a lot of people figure out when a piece of writing is bad.
I think this might be because rather than 'write how you talk', what you actually want to do is write how you would talk if you had time to say the best version of your thoughts. This means if you couldn't see yourself sitting down and saying the stuff you're writing to somebody, it's probably no good. If what you write doesn't have a natural flow when spoken from the tongue, it probably won't when people read it either.
I sometimes use this when not writing anything that is destined to directly go to other people in order to help my understanding. When working on a confusing problem I try to write it down as if I was explaining it to another person, and verbalise in my head what I have written (I'm liking the TTS solution someone mentioned elsewhere in the thread, I might have to bring some headphones into work and try that). It is surprising how often making myself write down the problem as if explaining it to another person makes the blindingly obvious solution that I'm until that point missing (or just over complicating) jump out.
Thinking of the problem as if you have to explain it to someone (even if that someone is an imaginary friend version of myself) forces me to organise my thoughts in a more structured manner (this leads to that which causes the other because of the thing that does the things to the other things so I considered that update but that would conflict with function X... - for more complicated things I'll even draw myself a diagram) which highlights the parts I'm skipping over but shouldn't be.
My adage has always been "if you can't teach it to someone with a minimal background, you don't really understand it." If I really need to study a topic, I prepare as if I was going to give a lecture on it. That usually makes it painfully obvious where the holes in what I know are.
I use Text to Speech to listen to all my posts before I submit them. I also use TTS and read at the same time to improve my attention. TTS imposes a constant pace and makes the message more pregnant.
I recently received a lengthy email of minor grammar errors in a programming manual I had written. I thanked the diligent bug reporter, and expressed surprise that so many mistakes had gone unnoticed for as long as they had. He told me that he was blind, and rather than reading the manual, he listened to it through a TTS system, thus catching some problems that might have been easy to miss visually.
This is funny, perhaps like others here, I find I usually have to reduce the complexity of my speech compared to my internal dialogue: particularly in using more commonplace vocabulary. Sadly barely anyone I know (including my wife) understands half the words I use. Indeed sometimes I don't really grok them myself; my brain just finds them most apposite.
So should I write as I [find I need to] speak or should I write with my natural lexicon?
I think so, but I was more thinking about what people actually do when you tell them "write like you speak." Most people I've seen then proceed to dump stuff onto the page and it's even worse.
The advantage of reading it out loud is (I'm guessing) that you process it with a different part of your brain. When you just read it, the words are your own and you don't process it the same way, whereas when you hear it the words in a sense sound external and it is easier to hear where it sounds awkward.
Thomas Mann did that (among other authors). He used to read his work to his family. Just look, how complex and hard to read some of his later work still is. And how complex the sentences are structured.
It is no guarantee, if you don't also think simple and clearly. But it certainly helps.
Yes, clarity is not always the goal in writing, especially fiction. I can imagine Mann sitting down reading his drafts to his family, who are all staring blankly at the ceiling, anxiously awaiting the end.
I think this is more of a technique to help people recognize when what they have written is bad. All too often do I get a student who is perfectly well spoken and who has obviously edited their work turn in something that is a mess. When you point out mistakes, they are usually like "wow, how the hell did I overlook something like that?"
It can be hard to recognize that something we wrote is bad, because we know internally what it's supposed to say. Something about the verbal and auditory processes in our brains seem to help bypass that though. It's by no means the only thing needed, just helpful.
This right here. Anything I've written is read out load, and it's astonishing how many unclear sentences, head smashing obtuseness and general rubbish this picks up.
However, one thing I have found almost universally helps my students is similar: read what you have written OUT LOUD. Is it halting and hard to read? Confusing and obtuse? Then you should probably fix it. There seems to be some magic about actually speaking the words out loud (as opposed to just reading it like normal editing) that helps a lot of people figure out when a piece of writing is bad.