As far as I understand, the 4th Principle demonstrates what animating technique you will use in the creation process. There are two to be sure;
1: Frame by frame/Straight Ahead animation. This particular technique has the animator create his scene one frame at a time, with no forward planning. The effect achieved is usually more natural and better paced so it’s better used for animating random effects like explosions or fire. It’s easily done when working on your own, however, sometimes the scale or shape of certain objects can become distorted, it is also difficult to amend mistakes that you notice later on. Don’t expect to get much work done with a team however, as you can’t telegraph what you want to happen, so everyone else will just have to stand around and wait for you to finish.It quick example I made in Paint showing the basic procedure. Note how the size of the running man has changed somewhat.
2: Key Framed/Pose to Pose animation. This method involves only drawing your character at significant poses and leaving a certain number of frames between each key frame. It’s great if you are working with a team of people. You can draw up the initial Key Frames, and then delegate the inbetween frames to the rest of your team getting a lot of the work done much quicker. Drawbacks however, can give the animation a mechanical appearance, making it seem devoid of that spontaneity that can be easily gained in frame to frame. Also, if the inbetweening isn’t done correctly, then the keyframes can seem to “jump”. Which brings us to forward planning, you HAVE to plan out your actions when you’re key framing. You have to know just how many frames should go between each pose. So for instance, if a man is moving from a crouched position to a standing one, he may need about 15 frames if he’s doing it at normal speed. Maybe 10 frames if he’s doing it in a rush, and possibly 22 frames if he’s moving very slowing (such as because of an injury).
There is a 3rd to take away from this, combining the elements of the two. The best of both worlds, though it can be difficult to strike a balance between planning and spontaneity. It also increases the work load as, you have to animate over the keyframes with what you have going on the inbetween frames. Which can sometimes lead to errors, especially if the key frames are quite far out. It’s the kind of thing I’ll learn through experience I wot, rather than by reading a book.