What does my banner need to have on it?
Your banner is the shop window to your channel so it must support what you do and how you do it. The imagery must be attention getting and display all the necessary things that your visitors need to know. Social media, channel links (no need to advertise your twitter on your twitter page nor twitch link on your twitch) and any other important info. (sponsors/teams/groups)
The style of your banners must be reflective of your logo to maintain your brand identity. (same colors, same design elements, same fonts)