If you’re just starting out developing your Facebook mission, one great place to start is with your fans’ expectations. What can your fans expect when they become a fan of your page? One optimal place to display expectations is on a custom welcome tab so all of your new fans will know what to expect before they start engaging on your wall. The following example is from the Facebook page of Pam Hendrickson Consulting.
According to Facebook, your cover photo is displayed at different sizes on desktops and on smartphones — 820 pixels wide by 312 pixels tall on desktops and 640 pixels wide by 360 pixels tall on smartphones. If you want to use a single image that works pretty well on both desktop and mobile, I found that 820 pixels wide by 462 pixels tall seems to be the best.
You'll want to pick a profile picture that’s easy for your audience to recognize -- anything from a company logo for a big brand, to a headshot of yourself if you're a freelancer or consultant. Being recognizable is important to getting found and Liked, especially in Facebook Search. It’s what shows up in search results, pictured at the top of your Facebook Page, the thumbnail image that gets displayed next to your posts in people’s feeds … so choose wisely.