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?)
I've been investing in stocks (occasionally) and mutual funds (consistently) for about thirty years, and I endorse Vaniver's advice heartily. I think overall, I'm up on stocks, due to doing most of my stock investing in cyclical stocks that I can buy and sell repeatedly over the course of many years. This has worked for me with both SGI and Cypress, which I repeatedly bought at low prices and sold at high prices. If you try this and find that you're not buying low and selling high, then you should stick to mutual funds and a buy-and-hold strategy. I've dabbled in other stocks where I thought I knew something and could time it, but few of those have turned out well. Happily, I knew I was dabbling, and kept the amounts low, so I got a valuable less for a relatively low price.
Mostly, I invest in mutual funds. I have subscribed to a newsletter that specializes in rating No Load funds (there are a couple). This gives me a monthly opportunity to review the performance of the funds I'm invested in, so I can tell when they stop being in the top performers and roll my money over to a different investment.
I record the monthly performance of each of my investments in a spreadsheet (used to be a paper notebook). The newsletter tells me which quintile the performance is in compared to the fund's peers. I highlight 1st and 2nd quintile in green, and 5th quintile in red. When the number of reds gets to be high compared to the greens, I look for a different fund with better recent performance. The commercials always say "past performance is no guarantee of future returns", but it's the only indication you can use. Most of the time performance is consistent over periods of a few years, so you have to look back a year or so when evaluating, and monitor continuing performance in a consistent way.
This whole process takes far more attention than most people are willing to put into it (a few hours a month on an on-going basis, and several hours every six months or so when choosing new investents), and few investors do even as well as the rate of growth of the broad market. That's why investing in the S&P 500 or an even broader market index is a good idea. If you put your money in a broad index and let it sit, you'll do better than 3/4 of investors.
Vanguard is only one decent brokerage. I personally use Schwab, but there are several others with reasonable prices.