I created this banner — native size 1500 X 500 pixels — to be used without modification on both websites. On Facebook, which employs a differently-proportioned image, the banner needs to be nudged to the left to show the entire book, and that’s built into the design. The lower left corner in both applications (FB and Twitter) needs to be empty to allow space for the round profile pics.
Tricks of the trade: That’s not really a photo of the book. I used an online 3-D book-cover simulator to do the magic. The lower left corner of the graphic also is the center of the “vortex” in the (subtle?) background image. Does it move your gaze toward the profile photo? That’s the idea, anyhow.