So far I found very few technical information on how to animate.

Like these links.

https://www.youtube.com/watch?v=P3E1FFDNnZI - TVPaint 11.0.8追加機能解説(6)塗りつぶしとカラーチェッカー

and

https://www.youtube.com/watch?v=dikKmj-55Vw&t=312s - How Suesawa works with TVPaint to make FLCL at Signal MD studio