Hey there! I‘m currently studying animation, so hopefully this will help some.
Just to begin, it was a good video. I like that is was short. A lot of people can tend to make them too long and that gets obnoxious. Quality over quantity. Also a quick note, my audio isn’t working, so I’ll just be talking about animation.
As for smoothness, I definitely suggest looking at the 12 principles of animation:
1. Squash and Stretch
2. Anticipation
3. Staging
4. Pose to pose
5. Follow through and overlapping action
6. Slow in/slow out
7. Arcs!
8. Secondary actions
9. Timing
10. Exxxxaaageration
11. Solid drawing
12. Appeal
These will definitely help give your animations more form and believability. For example, most everything in life naturally moves in an arc. If you lift your arm, it moves in an arc, not robotically. Hence, things don’t tend to go in straight lines. Of course, every animator is different. You might not being going for that kind of look, so do whatever suits you best
Good luck and I hope to see more animations in the future!