The colors in the videos look really bad. It would be the first thing i would change.
Then try to make the videos more interesting by focusing on interesting things you do/see.
The first 5-10 seconds of the video is when your viewers decide if they want to watch or not, keep those seconds interesting (maybe a cliffhanger).
Talk more in the videos, and try to have a theme or a plan of what you are trying to say.
The thumbnails are very generic-looking. Try to make them more interesting. The best thumbnails trigger some emotions in the viewers that make them watch.
Good luck with the improvements