I am beginning to suspect that it is surprisingly common for intelligent, competent adults to somehow make it through the world for a few decades while missing some ordinary skill, like mailing a physical letter, folding a fitted sheet, depositing a check, or reading a bus schedule. Since these tasks are often presented atomically - or, worse, embedded implicitly into other instructions - and it is often possible to get around the need for them, this ignorance is not self-correcting. One can Google "how to deposit a check" and similar phrases, but the sorts of instructions that crop up are often misleading, rely on entangled and potentially similarly-deficient knowledge to be understandable, or are not so much instructions as they are tips and tricks and warnings for people who already know the basic procedure. Asking other people is more effective because they can respond to requests for clarification (and physically pointing at stuff is useful too), but embarrassing, since lacking these skills as an adult is stigmatized. (They are rarely even considered skills by people who have had them for a while.)
This seems like a bad situation. And - if I am correct and gaps like these are common - then it is something of a collective action problem to handle gap-filling without undue social drama. Supposedly, we're good at collective action problems, us rationalists, right? So I propose a thread for the purpose here, with the stipulation that all replies to gap announcements are to be constructive attempts at conveying the relevant procedural knowledge. No asking "how did you manage to be X years old without knowing that?" - if the gap-haver wishes to volunteer the information, that is fine, but asking is to be considered poor form.
(And yes, I have one. It's this: how in the world do people go about the supposedly atomic action of investing in the stock market? Here I am, sitting at my computer, and suppose I want a share of Apple - there isn't a button that says "Buy Our Stock" on their website. There goes my one idea. Where do I go and what do I do there?)
There's your problem right there. Optimally, public speaking should require very little on-the-spot thinking with respect to word choice. Depending on exactly how important (and predictable) the subject matter is, you should have a relatively set vocabulary and set of concepts you wish to discuss. There's being competent at public speaking, and there's being good at public speaking; this comment is about how to do the latter.
Before I get started: one general useful piece of advice: if giving a speech, your first few sentences matter far more than everything else, because people will decide whether or not they want to listen to you and will frame their understanding based on it.
If you're giving a speech, you should have a moderately detailed bullet-point outline of what you're going to say, and you should have thought (or actually spoken) your way through it in advance. (Often many, many times)(In some cases, and for some people, it's ideal to have a verbatim script. But such circumstances tend to be relatively rare.) When you are actually speaking, you shouldn't need to think too hard about your exact word choices. For relatively high-stakes public speaking, I will have thought the issue over so many times it takes some effort to prevent myself from saying what I've been thinking of saying at a hundred miles an hour. In other words, if you're doing serious public speaking, you should be clear enough on what you want to say in advance that you can afford to devote a significant amount of your mental effort to your tone, movement about the stage, and speed of speech. This is admittedly advanced-level, but it's how one excels.
When answering questions (as opposed to controlling exactly what you say) it doesn't change much. 90% of questions can be easily anticipated. The remainder, you pause a bit before answering (or, if appropriate, reframe (honestly) to make easier to answer, "If I understand your question, you're asking _").
If you'll forgive a rudimentary sports metaphor: when you're throwing a ball, all you want to have to think about is where you want it to end up and how fast you want it to get there. Knowing how to position your arm and move your wrist and rotate your shoulder should be second-nature. You get them in line by practicing them before game day. Similarly, quality public looks off-the-cuff and conversational, but reflects a great deal of preparation and mental weight-lifting that prepare the speaker to communicate effectively.
[I'd certainly be willing to expand this into a top-level post if anyone thinks such would be useful. Public speaking skills are surprisingly rare; I believe this is because they require practice and people identify as being bad at them and avoid said practice.]