:D;)
Anyways, thanks for all the advice so far.
See also Sailboat’s entry.
But read good, reliable stuff, if you want the real answer. Professionally peer-revied and vetted stuff- like journals you read in college, textbooks (college ones, not grade / high school.) Find an author who KNOWS his stuff (read Hawking’s mass-market books on Astrophysics- turns out he knows his stuff), and has the credentials to back it up.
The internet mostly makes one dumber, unless you know the keys to finding the good information- who is the author? Are they trained in the topic they are covering? (don’t read the worlds greatest Medieval Historian if he writes a book about Pearl Harbor- as a professional historian I can asssure you it atkes years of research to get a handle on one era, let alone two!). How was their work received by others? How old is it: newer beats older, as a general rule… etc., etc.. I teach a 15 week course on how to do research and use sources, so this is VERY truncated.
Read good, reliable stuff, read good, reliable stuff, read good, reliable stuff. There really isn’t any other way.
Oh yeah- doubt what you’ve read, until you can confirm it in multiple places. Skepticism, critical thinking, and “smarts” go together!
Listen more; talk less.
Lots of good stuff here. And despite what AK84 said, starting this thread is a good first step. Self-awareness is a wonderful thing.
Having said that, you can certainly come off as less ignorant by stating your ideas as just being your perspective, rather than as inviolate truth. If you offer something as “My experience of that is…”, you’ll avoid a lot of grief.
Wise words. And you’re dripping all over the carpet.
And season that with real-life observation as well.
Good point. You don’t want to be so book-smart that you can’t relate to the real world.
One of my former teachers once said, “You have two ears and only one mouth for a reason.” 
Yeahbut it all falls apart with – ten fingers, one keyboard.
Be curious. About everything. For most subjects, assume you really don’t know what you’re talking about, but devote yourself to learning more. When it comes to personal experience, assume others have had different experiences and have come to different conclusions. Listen especially hard to the voices of people on the fringe - their story hasn’t been told as widely or as often, but that doesn’t mean it isn’t equally valid. Value the truth over being right, and when these two things are at odds, admit it.
This may not answer directly what you’re asking, but it’s something my father told me long ago. There are several versions at Knows and Knows Not (variations) and other websites as well, but the version I heard was:
Zeldar, that sounds a lot like the Johari Window. Except that it would look better on a bamboo wall hanging.
Frylock had some good advice in another thread you started:
I would generalize this to say that the way to be less ignorant is not just to memorize a whole bunch of isolated facts and aphorisms and bits of knowledge, but to learn about things in context and see how things fit together.
The more you learn about a subject, the easier it becomes to learn yet more, because you have something to link your newly-gained knowledge onto, a framework to fit it into.
Recognising your own ignorance is a wonderful thing! 
For one thing, because at least you are going from an “unknown unknown” to a “known unknown”. You know that there is stuff out there that you can come to know more about! (Similar to what Zeldar says.) Well, if you didn’t at least realise that you’d still be stuck in the mud.
For another: the Dunning-Kruger effect. Incompetent people tend to overestimate their skill. Being aware of at least some of your own incompetence is an advantage.
I am ignorant too, that’s why I’m here. I post mainly to give my opinion on things I am less ignorant about, and then just read a lot. Sometimes I post, then it turns out I was ignorant after all. Oops. Sorry WhyNot. But, hey, at least it cures the ignorance bit by slow bit.
I’m pretty sure no regular posters came here because they knew everything already and wanted to help out the poor ignoramuses. Most came here because they read something by the Master that they didn’t know yet. Many because they googled something they didn’t know. But we certainly all have some ignorance left to be fought.
Edited to add some Shakespeare: “The fool doth think he is wise, but the wise man knows himself to be a fool.” We can always do with some Shakespeare 
You don’t have to have an opinion on everything. You don’t have to have a wild-ass guess for everything either. A mature person is comfortable enough in their intelligence to admit that they don’t know or that they haven’t made up their mind. There is nothing wrong with being an agnostic.
And even when you find it extremely difficult not to form an opinion, you can still just keep your mouth shut about it. Sometimes its best to keep even “good” opinions to yourself.
When Socrates sought to examine, he asked a lot of questions. You saw how that worked out for him.
Let other people ask questions. When you have a question, give other people a chance to, and - this is really important - ask yourself why they’re asking the questions they are, and why they aren’t asking the one you want the answer to.
If, after some reflection, you still want your question answered, ask it. But listen, and listen actively.
I think your problem, specifically (and don’t take this as a slam) is twofold: you push too much (and dig yourself deeper), and you don’t know when to defer to authority.
For the first, you can just let a topic drop. You’d get attacked a lot less if after being proven wrong you would just stop defending yourself. Don’t post a 3-page post explaining why your smart phone made you wrong, or how your history book mislead you. Just say “okay, fair enough” and move on. Insistence of defending yourself on matters that aren’t worth it (obviously don’t compromise your morals, or when you’re a legitimate expert) makes you look ignorant.
The second is related, it takes a long time to realize who the expert is on what, and I don’t know everybody here, but I wouldn’t give any major mathematical quibbles against Indistinguishable – or attempt to argue physics with Chronos. Remember that a few months of actual experience, even with months of internet research, is not a substitute for the real thing. That’s why you got slammed when you were arguing with a Career Taekwondo instructor about Taekwondo. You may very well have been right, I have no idea, but unless you have some damn good and reputable cites (and for something as fluffy as “what a dojang should do” I doubt there’s anything that authoritative) you really need to defer to authority.
You seem to like Socrates, and I believe you know that Socrates is the wisest man because he knows that he knows nothing, correct? It’s true – the more you know about a field, the more doubt you feel. It’s natural. Even though I probably know a whole lot more about Computer Science than most people in the world (since most people have never touched the subject), this also means I know how many fields there are in Computer Science, and how deep those fields are. I also know when I’m not an expert. I’m not about to argue the most basic of Compiler Theory, and even though I’ve TA’d the subject, I’m barely more than a novice on the subject of AI (except perhaps Transfer Learning).
You have to accept that at your level of education, you simply cannot give an authoritative answer on most anything. Maybe violin (I think it was violin) playing, if you’re really that good. It also means that you have to recognize when you’re outclassed and not argue with people who outclass you on the subject.
Being less ignorant is just a matter of listening, reading, learning, and participating. Seeming less ignorant is primarily a matter of knowing when you’re beat.
Live with your eyes and ears open, and try a bunch of widely-varying stuff. With an emphasis on “live.” A teenager simply cannot have the breadth of experience that someone twice their age has, assuming the older person has done what I recommended in my first sentence.
In my early 20s I had a boss who, no matter what subject came up, could join in a conversation about it and contribute something constructive. Basically he seemed to know so much stuff. That’s what I wanted to be able to do. And guess what, a quarter of a century later I can. I’ve travelled a lot and tried to get at least a tiny bit of experience in lots of things (not to become an expert in any, but just to know what they are all about), even if it was something I wasn’t particularly interested in.
My general advice for fighting ignorance (and I’m advising myself as well) is to assume nothing, especially don’t assume you know more about a topic than the other people in the conversation do. Also, remember that everyone has a story and that generic, boring person you’re talking to may very well be much more fascinating than you think, or have lived a life entirely different than your own experience. We are vastly more different than we assume, and we are vastly more similar than we assume.
Missed the edit window. I wanted to add:
And be aware of it when you don’t know about something, or know less than the person with whom you are conversing. Don’t fake it; you will always be found out by someone who actually knows their stuff.
It’s like young children who think their parents can’t tell when they are lying, except when it comes from an older person it’s embarrassing.