Yesterday Twitter revealed a new look with a much bigger header and the ability to pin a tweet. The new look is visually more impressive and allows for tweets to be highlighted. This new look is available for new accounts right now, but older pre-existing accounts will have to wait for the new look. The new look is only visible to desktop users, while mobile users will still see the older look.
Twitter has a recommended size of 1500×500 pixels, that doesn’t work very well. I found that the 1920×640 template works better as seen here: