Animating (+ Commentary): Discovering Key Framing in MS Paint

Note 5-13-2020: I used to call this a tutorial, but I'm still coming up with new tips that are sometimes better than the ones I gave before, and I'm bad at teaching on the spot, which was what I tried to do here. Now when I explain what I'm doing in a video, it's mostly for commentary, without the "you have to" or "you should."
Update 10-3-2020: Here's a playlist of every animation commentary, including better, recent ones:    • Drawing/Animating - With Commentary