Loops and holds are two fantastic cheats to help you tell your story with less work.
also known as cycles
A loop is simply the same sequence of animation repeated over and over. Used carefully, loops can stretch out your animation really effectively, and you can make one if the first frame of an animation is (nearly) the same as the final frame.
Loops are the drawn animator's greatest friend, but are more difficult to create in stop-frame, cutout, and pixilation. However, with careful planning - or with desperate use of the 'ping-pong' loop in the edit suite! - remarkable things can be achieved.
A good example of a straight loop is a wheel turning or a dripping tap.
A good example of a ping-pong loop is a clock pendulum. You only need to create one set of moves, in one direction, to create the 'tick'. Then, usually in the edit, you reverse the movement - to create the 'tock' : and then keep moving back and forth: tick-tock-tick-tock!
The main problem with creating a loop is too much going on - eg someone has created a fantastic dancing bear sequence that you identify as ideal for looping. But there's a bird flying into the background, and when you try and loop the dancing bear, the bird keeps on entering and re-entering the screen!
Good animation is like a raisin sponge cake; you can get away with a lot of minimalism (sponge) as long as you reward your audience occaisionally with tasty dynamic bits (raisins) - John Challis
Holds are simply pauses when you don't animate anything - they are that simple. For example: when a character turns and looks, you simply pause the action at the end of the head turn. This can be achieved by recording one or two seconds without changing anything, (If you are working on 'threes' you just press the grab button maybe ten times) and this hold is easily shortened or lengthened at the edit stage. If you forget a hold - this can also be created in the edit by using a freezeframe or still feature.
In drawn animation, a hold does not work so well when a drawn animator's style is very wild - see 'boiling' below.
'Boiling' is where you trace the same drawing almost identically (usually 3 times) and then film each in turn and loop it continuously. This adds life to a scene that doesn't actually have (or need to have) anything moving in it.
It can be difficult to convince young children that boiling has any value, but sometimes without it, a wild animated style will sometimes not tolerate a hold.