I found tutorials by these authors on various Tumblr blogs. In addition to being informative, their art style is really cool!
Ah, about saving video in frames: in Krita you can do this by going to File > Import video animation. It also accepts gif animations.
Before I extracted frames from gifs by Gimp, I gave up because some of the frames came out corrupted. In Krita it always works fine! 
Much as I love color and drawing, it’s composition that gives me the most satisfaction. I have no idea if I’m doing it “right”, but I sure enjoy positioning the image elements, moving them about (sometimes by seemingly tiny amounts), erasing and re-shaping them. When a scene feels “ready”, I can find all kinds of balances and symmetries in it, very pleasing. Frequently I’ll try to echo the compositional balances with color balances. I’m certainly not always successful, but luckily I get a lot of fun just out of the attempt.
Yes, composition is one of the keys: if it’s not correct, it ends up affecting the entire art, even if it looks realistic.
I’ve always gone with these four basic rules which are a distilled version of Edgar Payne’s, per a previous poster. Horizon (either high or low); golden ratio where the focus is on one of the four key points when a canvas in divided into thirds; focal point where a viewer’s eye is drawn into a point via angles; and off balance where the contrast between large and small focuses a viewer. On my square works, composition looks like this …
New Link!
• Composition- How To Make Pictures - a post from Animation Resources website, containing tips on composition.
