Fall is officially here, so in the spirit of the Back to School season, here’s a quick lesson for you on some of the changes and trends you need to pay attention to on social media. Let’s get to work: 1. Twitter has a new header image Launched on September 18th, Twitter introduced a headline image, similar to that of Facebook and Google+. The dimensions are different (1252px X 626px for optimal viewing across all devices), so you you can use an image that has a…