Well there are a couple things.
- your banner, personalize it to fit your channel.
- your avatar, make a custom avatar to fit your bannet and make it more personal instead of a internet picture.
- Your about section is a bit empty, use it to tell about yourself and channel.
- you already named thumbnails yourself.
- Maybe add a channel trailer to the home section?
- You can add playlists like populair uploads and such to the home page to keep it clean and ordened.
- Video description, use it to give a detailed description about the video's content.
- Playlist description, add a detailed description with what th playlists contains.
Good luck and hope it helps
As for thumbnails and banner i could advise GIMP, very easy to use.
For an avatar you could use basic apps like FaceQ as i did for my avatar to give an example
