In the past 5 to 10 years, social networks have grown to such epic proportions, that pretty much any person in the developed world is on at least one network (with many people joining more than one social network). Although being on Facebook, Twitter and Instagram have its own benefits, there are also many negative aspects - for example, many people say that you should post things that you are going to be ashamed off in the future.
It is a well-known fact that thieves love to use social networks, as many people post about their vacation plans. That gives criminals a lot of amount of time to determine where you live, and how to enter your home once you leave for your vacation destination.
While most people you are going to meet in your day-to-day life are going to be normal, upstanding citizens, there are still some people that could be classified as "stalkers," or something similar. Posting your location online can act as an invitation to such unwanted attention.
Some phones these days are so advanced and full of processing power, that they can even embed your exact GPS coordinates in the hidden EXIF information of your photos. That can be bad, as some photo sharing services do not remove EXIF information, meaning bad people could be able to see where you live, or where you go out.
Depending on the country or state where you live, there could be laws against filming people who haven't given you the permission to do so. In fact, in some jurisdictions, even your friends could be able to sue if they later decide that you've filmed them without their permission.
Some people get so excited when they receive their Master Card Platinum card, that they sometimes even try to share the news (together with photographic evidence) on social media websites. That could be a very bad decision, given how rampant credit card fraud is these days.
It is normal to learn about certain news about your friends, that is simply going to blow your mind - like if a friend got engaged, pregnant, or got a nice job. In these situations, it is better to leave your friends to be the ones to the first post the news.
While it is great to post photos of the outfit you wore last-night and stuff like that, it is still important to keep in mind what kind of photos you want to post online. Sometimes, if you post to much, that could cause remorse years down the line.
This paragraph is similar to one of the previous parts about revealing credit card information on your social media accounts. The same goes for banking information - you have no idea how clever thieves are these days, and even your IBAN code could be enough for them to steal money from you.
It is normal to frustrate with your job from time to time. However, it is best to keep those kinds of thoughts among friends and family, as some bosses and colleagues could get offended by your disparaging social media posts, which in turn could make your job even worse.
Politics is another area that could cause a lot of controversy in your life. The worse thing about political controversy is that you don't have much to gain from posts like that - in most cases, posting about your favorite politician could only cause you to potentially lose friends.
Many comedy movies and standup comedians have showcased how funny off-color jokes can be. However, to properly deliver a joke, you usually need to use your body language and vocal tonality - something that isn't possible to do on social media.
Fights and arguments with your significant other are another part of your life that you probably shouldn't share online. The reason for that is that many fights will pass away, and your life will return to normal - so why leave a permanent mark online?
Some people use the so-called "grandmother" test to decide whether they want to post a certain photo on social media. While party pics are okay for online posting, you should still test them with the grandmother test, so you can be 100% you are okay with the pictures.
You might not be thinking about much when you are taking a selfie picture, but the fact of the matter is that it is simply not appropriate to take a selfie in sacred and serious places (like the above photo shows - during a funeral).
Posting unsubstantiated accusations can be a terrible thing to do online. Not only could you be wrong, but you could also get sued with a defamation lawsuit, because in most jurisdictions, posting factually incorrect information is a form of libel.