animation techniques

As you can see from this video, made on Toon Boom V.3, that the balls squash and stretch are rather exaggerated. In real life a ball would not quite bounce like that or squash like that, its exaggerated for comic effect.
You will find this technique is proven quite popular amongst animators, its helps make an object seem 'alive'. Though for rigid objects like chairs and tables this rule does not apply, unless it is the wish of the animator to make them 'alive' in such a way that it requires a squash and stretch.

Disney, though a fan of realism, tended to make use of squash and stretch techniques to make objects, characters and cartoons have a more comic effect that the audience would like. He started this trend with the seven dwarfs, giving their movements are more comic feel.

Arcs:
But another aspect of this animation is the curve or arc that it is following. Object dont move in straight lines. For example, if you move your arms from your head to you side its an arc movement you make. So by giving your objects an arc to follow its make more realistic. For comic effect the arc may be discarded, but it has to be done very well otherwise the audiences wont like it.

One thing to remember whilst animating is that whatever you animate will keep the same volume as when you started. It doesn't change, if it does halfway through your animation your audience will notice and it will be taken as a mistake.

Exaggeration:

Exaggeration is used to express a characters range of emotions and characteristics. But as the rule for stage goes;
'exaggerate you actions and re-actions by 10'
The same rule applies for animations. The reason we do this is simple, its makes it easier and clearer for an audience to understand that a character is expressing an emotion. Like anger, if they a really angry they will tend shrink into themselves, shaking and their entire face going red, or the ever so popular steam coming out of the ears, like we do this in reality-no, but it does get across the point of anger as well as adding a comic effect to it all.
But then again this element has got to have a balance, although it is good to exaggerate certain scenes or emotions, take care not to do it too much as important scenes that require little actions and more sympathy will be drowned and wont make any impact at all.
So balance is also a required element.

Anticipation:

Anticipation, a technique used to prepare the audience for what is about to happen next. There are 3 stages:

-before
-the action
-the end

As stated before it usually used to prepare an audience for what is about to happen, usually before an important event. For example, when someone is about to throw a ball there goes back in arc, then forward again, then at the peak of the throw/arc they let go.
How do we know what action they are doing, through anticipation. By watching where his arm is going we assume the next course action, which be throwing.
But not only do we anticipate from these actions what will happen, we anticipate how it will happen. If the throw is done with sheer force (for example in a game of baseball) you see the body curl into itself then let go with amazing speed hurling the ball forward. We anticipate from the persons body action the speed and strength of the throw.

This applies for all actions, whether they be big or small in animation. Anticipation is an important technique that allows the viewer to get more involved with the animation itself.