There are lots of things to take into consideration when you are deciding on poses. First and foremost, there is the character’s personality, physical traits, and usually a library of movements for that character that provide information on how they move, such as walk cycles, postures, etc, and a character “bible” that you can access at the studio. Those things should always be studied very carefully when you are working on a show so that you have a strong sense of how the character moves.
And then, of course, there’s the story. What’s happening in the shot? What emotional state is the character in, and what actions do they need to achieve during those frames? What happens in the shots before and after the one you’re animating? These questions will have to be kept in mind so that the action you create in your shot fits well in the overall story arc. Is the action in the shot more extreme or subtle? If it’s more extreme, the poses I create are more opposite in juxtaposition to each other. The opposing body lines will create a lot more energy and momentum for a high-energy shot. If it’s a quieter shot, the poses will have less opposition.
The poses need to very clearly communicate who the character is and what they are feeling at that point in time. Remember, once the shot is playing, those poses are only showing for 1/24th of a second (except in the case of holds of course, but you know what I mean)! The biggest thing to keep in mind is that good poses will create a very individual personality in the character, rather than just creating generic movement.