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?)
You have to put yourself in environments where you'll be able to interact with a lot of women. College is in a lot of ways set up perfectly for this: if you're not in college right now, consider joining a class or an activity group. Try to make it one where the gender balance will be in your favor. Book groups are one example--they're wildly tilted towards women (I suspect men just, you know, read books, and don't tend to see the value in sitting around sipping coffee and talking about reading books). But if you like girls who wear glasses, try finding a congenial book group. You'll probably be the only man.
Even better than book groups, though, are dance classes. Swing and rockabilly aren't super trendy anymore, but the scenes still exist in a quieter way, and these classes are great for single men: a) they're filled mostly with women; b) dance is an inherently flirtatious activity, and the physical leading/following dynamic is one that many women find very sexy; c) even if you don't find a date in that class, you'll have learned an attractive skill, and you'll be able to participate in events that will introduce you to more women; and d) physical exercise is good for building both confidence and sexiness. Yoga classes might work too, or if you can find a martial arts practice that attracts significant numbers of women (maybe check out your local aikido classes?).
The SCA (Society for Creative Anachronism) is also a surprisingly good choice for geeks who want to hook up. Wearing princess dresses is enough of a draw for women that the gender balance, while tilted towards men, isn't too awful, and so many relationships get started in the context of SCA events that there's a joke about it. (The joke is that "SCA" actually stands for "Society for Consenting Adults.")
There are of course singles bars or activities like speed-dating that are specifically designed to let you meet single women, so you could try those too. A lot of people find those environments stressful and frustrating, which is why I'd suggest finding a social scene that is not specifically about dating.
Lastly, let all your friends know that you're interested in meeting women. Ask to be introduced to their friends who are single. This is how people used to meet each other and it is still an important avenue to keep open.
You have to ask women out on dates. This part, I know, is hard, and I'm sorry to admit that many women don't even understand how hard it is. You will be rejected and it will suck every time, but this part is a numbers game. You just have to keep doing it until you find the girl who says "yes."
The pre-reqs for asking a girl out are fewer than you might think. It's best if you have already been introduced and have interacted a bit in a friendly manner. When I say a bit, I really mean just that you've spoken a few times. It is far, far more common for geek guys to err wildly in the opposite direction. Don't do this. If you like her, ask her out, and make your intentions unambiguous. The sooner the better.
If you're following my advice and meeting girls in activity classes, you would do this by approaching her just after one of the classes, maybe as she's getting her things together or as she's heading out the door. Make eye contact and smile. Start with a compliment that references the interactions you've had--"Hey, I've really been enjoying dancing with you [or "sparring with you," or, "I really liked what you said about the book"] and I wonder if I could take you out to a movie next week."
Be really clear about the fact that you're asking her for a date. Try not to say something like "I wonder if you'd like to meet for coffee and talk " because she could interpret this as merely a friendly gesture on your part, and you don't want that. A lot of inexperienced guys think they should establish a friendship before they ask a girl out, but you really don't want to sink a lot of time and energy into a girl who is never going to see you "like that." (It is true that established friendships can make a wonderful basis for romance, but never, ever count on that happening.)
Also, propose a specific activity and a specific time. Don't just say "I wonder if you'd go out with me some time" because a) it sounds a little desperate and b) a lot of women have trouble saying "no" directly (we're socialized not to). Leave her a face-saving way to refuse. If she says "I'd love to but I've been really busy with work/school/life recently," that means no. Move on. (If, on the other hand, she says "I'm going to Guatemala next week, but I'll be back by the end of the month, maybe then?" that means yes.)
Dealing with rejection: When you are rejected, try to be gracious about it, even if she is not. Like I said above, a lot of women truly do not understand how much gumption it takes to put yourself out there by making a pass. If she seems annoyed or condescending or whatever, try to shrug it off; just smile and say "okay, no problem" or something along those lines. Do the same thing if she says "I'd rather just be friends." (But for the love of Pete, do not spend a lot of effort trying to actually cultivate a friendship. Moooooove on.)
It does get easier the more you do it. Just remind yourself that it is a numbers game. The worst thing that can happen is not that you ask ten girls out and they all say no. The worst thing is that you ask ten girls, they say no, and then you stop asking. Because whether it was Girl #11 or Girl #83 who would've fallen head over heels for you, you'll never find her now. Keep looking to meet women, and keep asking them out; these are the two steps that lead to relationships.
Troubleshooting: If you do find that you are consistently rejected, there might be something going on with your self-presentation that is offputting to women. Make sure your basic hygiene is good: that you are wearing clean clothes that fit you, that your hair is cut and that you are clean-shaven. (Facial hair is Advanced Fashion for Men: if fashion is not your ballgame, just shave, trust me.) Ask your friends if there's anything going on with your looks or demeanor that might be getting in your way.
If you are overweight, start an exercise regimen, but do not wait until you are at your ideal weight to start asking women on dates. It is perfectly possible for big dudes to find love, they do it all the time. It IS more important to make sure that you wear flattering clothing that fits you well--a baggy, threadbare tee-shirt and Hawaiian shorts may not cut it. Use Google Images to find pictures of some of the heavier celebrities (like Sean Astin, or Seth Rogan before he slimmed down). Check out what they are/were wearing, and use those pictures as a style guide.
You may also be acting in ways that indicate you don't value yourself, which can make women (and other people in general) instinctively shy away. You will probably need the help of people who actually know you to diagnose these kinds of problems and help you fix them.
In general, though, from my observations, most geek guys are able to get dates so long as they go where the women are, and ask them out. The most common mistake by far is simply failing to execute one or both of these crucial steps.
This can backfire if you live in a small town.