I don't think you can avoid risks and be vulnerable at the same time. It's a bit of a catch-22, I'll admit; oversharing can push people away, but the only way I know to figure it out is to fall, get back up, rinse, and repeat.
I would suggest that, like many things, that line is dependent on all of the details of the situation. Because all of those subtle details (e.g. the mood, receptiveness, familiarity, interest, etc. of the other person and yourself) matter, you need to be able to take those in and respond accordingly. So you could say that a prerequisite for connection is something like "presence", the ability to give your full attention to the interaction itself. Or you could say that this is actually the essence of connection, and the conversation is an expression of that togetherness of presence.
Just keep the conversation appropriate for time, place, and how well you know the person. That avoids oversharing.
For example, I overheard a conversation between two coworkers. One asked about a health issue and the other responded with this long drawn out story about an extremely gruesome injury with lots of details leaving everyone extremely uncomfortable. The other coworker complained about to me afterwards, because I overheard it.
He could have said "oh, I'm doing much better! Had a bad injury about six months ago that set me back some, but I'm healed up from that now, thankfully!"
Maybe there's a time and place to share the gruesome details, depending on who your friends are, but it's certainly not with a work acquaintance.
Depends on context. Learn to read the other person or group, there are cues. Also there is mutuality, back and forth.
I also question the validity of the cultural concept of "oversharing" being as always bad. Maybe it's bad by definition, but then what is "oversharing?" If you share am I allowed to give you advice?
my definition of oversharing is when the recipient signals that they are not interested. in other words it depends on the other. there is no general line, and each person is different. you never know. it also depends on the character of the recipient. you may tell me things that are way to personal that i am not ready to talk about, but i'll most likely ignore that unless you become obnoxious about it, because i find an offensive reaction to oversharing just as bad and i don't want to lose your friendship over your "mistake".
i'd also say that if someone you consider a friend turns away because of your oversharing, then they probably weren't a good friend to begin with. the only danger is if you tell someone something personal that they end up sharing with others, but that's a breach of trust by that person, not bad oversharing.
It’s all relative. You can share something slightly personal or controversial and see where it lands in the other person’s comfort zone. Then it’s up to you to decide what to do with that info.
You cannot over share Most people don't give a shit about you. And the ones who gives a shit does have their own ideas about you anyway. So you would be surprised how much influence you can do to change those ideas. Even if you change their ideas it's still an idea in your head as far as your are concerned.