I've written about using "The Test" before posting (or emailing, or really committing anything to permanency. It's good advice, and I stand by it. However I saw a post about what not to post to social media, and I think this adds some depth to my advice.
It's a more formal view of social media, and it's written more for businesses, but anyplace where you see it asking about followers, replace that with "future employers". If you see "mission", then think about your brand instead.
Everything you do on social media reflects on you, and if you have accounts on Twitter, Facebook, etc. where you are trying to grow your career, make sure you stop and think about what you are posting and what it says about you.
In general, I'd limit my posts to thinks I've learned, things I've accomplished, things I've solved, things I've done well.
I'd leave out complaints and concerns regarding coworkers and employers.