Blue Kite Stained Glass
It seems a simple thing, but getting the right element for your Social Media image and headers makes a big difference. This was a straight forward one as the logo fits nicely in a circle for Twitter and Facebook etc. But the logo still needs saving at the right dimensions, and must look good small on a smartphone, not just a big monitor.
Profile images - the big banner ones behind the logo on your profile page make a big impression, it's worth having a few to mix it up occasionally.