A picture is worth...a lot of 'likes'

Just like in print, the thing that will get you noticed on social media are photos. And to make sure your photos look their best, it's good to know a bit about the requirements of each social media platform. This article, on SproutSocial, gives you good information on sizing your photos to best show on Facebook and Twitter.
From Twitter to Facebook, Your One-Stop Guide to Social Image Sizes

Or here's a quick infographic with some useful information: http://www.cloudtactix.com/infographic-the-ultimate-social-media-size-cheat-sheet/

And connect your Instagram account to your Facebook page for seamless photo sharing.
How to post Instagram photos to Facebook