Squash & Stretch
This action gives the illusion of weight and volume to an object/ character as it moves. Also squash and stretch is useful in creating dialog. The use of this can vary from the bounce of a ball to the movement of a character.
This movement prepares the audience for a major action which is about to occur, Such as a character starting to run almost all real actions have anticipation this may be major or minor.
A pose or action should clearly communicate to the audience, The attitude, mood, reaction or idea of the character as it relates to the story. The effective use of long medium and close up shots as well as camera angles/ motion also helps telling the story.
Straight ahead & Pose to Pose
A transformation from one item to another, this may be a character twirling then changing clothes during it such as superman or perhaps a drone changing form.
Follow through & Overlapping
While the main body of a character stops motion the top of it caries on in the same way this can be a character running then suddenly stopping then leaning forward then they might regain balance, this could also give a clumsy feel to a character.
Slow in Slow out
A build up in speed then a gradual slowing down motion near the end its reminds me of ease in ease out.
All actions with only a few exceptions follow an arc or a circular path this is especially true with human motions as it gives the animation a more natural feel.
More than one action occurring at the same time as a secondary motion for instance the second motion may be because of the first action sort of a follow up actions.
Timing comes from your own experience and use of animation using trial and error as a refining technique. More drawings/frames make the scene slower and longer where as fewer drawings/frames make the scene faster
Makes an action seem far more supreme to what they should be For instance their actions or poses may be exaggerated to make their feelings and emotions more apparent to the audience.
The basics of drawing form weight volume, solidity and the illusion of three dimensions from using depth portrayed in the images 3D is movement in a 3d space and 4D is movement in 3d space and time.
A live performer has charisma, an animated character has appeal. An appealing animation does not necessarily mean being cute and cuddly. It could perhaps come in a heroic form or a shy scared manner. Basically a personality. The character should normally match the environment and story line.
Walt Disney made the 12 principles of animation hence my references to drawings, I also referred to frames.
Gif credit: http://the12principles.tumblr.com/
All text is my own work, my results may have been influenced from recourses found online.