With Alicorn's permission, I'm resurrecting this thread.
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.
I'll start off with one of my own: What kinds of exercise can I do at home (I do have 5- and 20-pound weights), and what are good ways to get motivation to do so regularly?
As RomeoStevens said, practice is your best bet, but even better is to practice with people who have a decent grasp of what prospective employers and HR people will be thinking while interviewing you.
There are surprisingly many community centers that offer direct training programs for finding good jobs and winning interviews, and they almost always include at least a little bit of interview practice. Up here in Canada, they're almost always free thanks to government funding, but for U.S. it'll depend on the local specifics, I'd wager. However, you want to be looking at the very local stuff, i.e. town/district or community newspapers, the city hall's list of community organizations, the local section/version of the "yellow pages", and so on. These are the places where you're most likely to find or learn about the kind of places / community centers that offer these training programs.
But again, the key point is practice and experiments with good feedback (most honest feedback is good feedback, but much more so if the other person(s) are experts in this, which is much more likely in the aforementioned community centers).
Live practice, as RomeoStevens mentioned, was definitely on my list of things to do to improve interviewing skills. Your advice about seeking out direct training programs was something I did not even consider, so thank you! That would indeed seem very helpful.