Revisit your Facebook cover image at the top of your Facebook Page.
Is it clear? Compelling?
What does it tell others about you or your company?
You need to be careful about how much text you add to your image, however, you can combine images to make an attractive first impression.
Consider creating different designs and change them out quarterly. Look how it compliments – or clashes – with your profile image.
Cover images are 851 pixels wide and 315 pixels tall.
More here from Facebook regarding their rules and specs for cover images: https://www.facebook.com/help/