Knowing what to say and post can be hard on social networks and doesn't come naturally to most people. Developing a persona that is detached from the real you helps that process but can take time. My suggestion is to first re-post content you find relevant and interesting. Favorite and like what you think is good content it'll help you get into the frame of mind to create your own content eventually.
When attempting to write a screenplay I was taught to make it relevant to current events and to stick a pregnant woman and/or dog/cat in it to help people connect with the story as those themes are universal. I've used the same formula on social media with great success. People love to see animals and babies. That's the basics of the human experience that translates well on social media platforms.