Professional Etiquette on Social Media

When social media first arose, many followed a certain professional etiquette such as not posting pictures in their swimsuits, not getting too political, and not posting details about where they lived. But today, the "rules" have changed drastically. In fact, do we even have unspoken rules to follow anymore? And with the expanse of different platforms, people often feel they can save the professionalism for LinkedIn, while letting their negative side out on Twitter and sharing every detail of their hotel room and brunch menu on Instagram. So while living amongst blurred lines, what should we be keeping in mind when posting?