It's a very difficult thing to avoid really, because the more you talk to someone, the more you're going to reveal to them, and the more they're going to learn about you, no matter how close-mouthed you are. At the same time, it's also impossible for someone to get to know someone else, because they only ever see what they want to see. In short, it's always going to be unsatisfactory, because what people learn won't be what you tell them, and their interpretation of what you DO tell them will be totally different to what you intended.
...and yes, I realise that is an extremely pendantic and evasive response to the question. So.
I've always been a bit of a paradox when it comes to this....I'm not particularly secretive with my personality or my views if I'm asked...and sometimes when I'm not. I've always been highly opinionated, and I'm not going to censor myself for anyone out of fear of being judged or misunderstood or anything like that: if people don't like the way I am, that's THEIR problem to work through, not mine. I am who I am. Deal with it, or don't. Either way, leave me out of it. I refuse to be bound by the expectations others have of me, and I will not take responsibility for the way my words are misinterpreted if that occurs, either.
But when it comes to actually TELLING people things, volunteering personal information, sharing my secrets or my concerns, confiding in others, the whole "friendship" thing...I'm as close-mouthed as they come. I don't allow people to get closer to me in that sense. At all. It's a completely shut door. People who try to get to know me in that sense are wasting their time; they've got more chance of turning back the tide with a spoon. I have numerous reasons for this. I don't particularly feel like sharing most of them.
As for me getting to know others...I tend to take people as they are. If they want to tell me things, that's fine. If they don't, that's fine too. I make assumptions the same as everyone else, and I may occasionally ask a question for clarification, but I don't actively seek to get to know people. I've reached a point in my life where I'm quite content with conversation and have no real need of that kind of intimacy...been there, done that, nobody bothered to buy me a t-shirt, etc.
tl;dr People know what I'm like, but they don't know me.