Hi there! Thanks for the great question!
Pantomime for animators is, essentially, the art of telling a story with the body, generally without relying on any dialogue. It's all about communicating as effectively as possible using the body language, timing, and face.
So, I'd say some of the most important things to keep in mind when diving into a pantomime shot may be:
1) CLARITY. This is SO number one that they should invent a number that comes before 1! This is your top priority, and every decision you make should be one that makes your actions and emotions ever more clear. That's not to say that every acting decision needs to be obvious or cliche, of course, but even within the complex subtlety of your performance, clarity should always be your primary concern, because if the audience misses an important action or misreads your character's emotion, then the performance is a failure and nothing else really matters!
2) Strong and dynamic poses. Particularly for action scenes, this couldn't be more important. You want the actions to not only be clear and read quickly to the audience, but you want them to be fun to watch! Dynamic poses point the way towards more dynamic and exciting actions, and the more exciting the action, the more fun it probably will be to watch it. This extent to which you can exaggerate this concept will obviously be determined by the overall style of the project (realistic vs. cartoony), but the definition of "what is dynamic" within that project is *also* determined by the style. In a more cartoony piece, you'll have to REALLY push the poses in order for a particular action to feel dynamic, whereas animated characters in a "realistic" film will feel dynamic for "half the price."
Either way, the point is to consider the most exciting, fun, and entertaining way to approach your pantomime shot, and particularly when dealing with strong actions (fighting, sports, etc), dynamic poses can often be your best friend.
3) Relatable acting choice! This is a part of clarity, but it bears emphasizing that you should make acting choices that will be recognized by the audience. While many gestures are culturally specific, many (if not most) are universal, so choose your gestures very carefully. The same thing applies to your facial expression work -- most facial expressions tend to be universal, so be sure not to get so caught up in "not doing anything cliche" that you end up choosing bizarre facial expressions that don't properly convey the emotions of the character.
4) Eyes. The eyes can help SO much in a pantomime shot, and without any dialogue, you should pay them extra special attention. The audience will look at the eyes FIRST for cues, so take that opportunity to grab the audience's attention and lead them through your shot. Let the eyes help convey the emotions. Let the eyes help your audience know where to look in the scene. The eyes can help you sell the joke, tell the story, or help us not miss an important action. Eyes are key! Film yourself *really* acting the scene out, and study what your own eyes do before caricaturing them in your scene.
5) Body Mechanics. In a shot with dialogue, the audio can really help you in so many ways. You have audio cues to tell you when and how to move the character. The words and subtext dictate the gestures. The spoken words can help you tell the story. In many ways, you can rely less on the body animation, and the audience may not notice some wonky mechanics here and there. If the character tells a funny joke, they may not notice or care that the weight is a bit off, for example.
But in a pantomime shot, every single pair of eyes is going to see that weight shift in the wrong spot, and while they may not know how to fix it, or even what feels "weird" or "fake" about the scene, they will feel the mistakes in their gut. In light of that, spend some extra time studying and planning the body mechanics of any pantomime shot so that you really nail the weight shifts, timing, lead and follow through the body, anticipations, etc. That stuff is KEY to selling a good pantomime shot.
6) Subtext. My last piece of advice would be to actually imagine that there are lines in the scene. Imagine the subtext. What is your character thinking? What is he feeling? You can even write some lines of dialogue and record yourself performing them, if you like. This may be very helpful if you feel like the "blank slate" of an audio-less shot is intimidating and holding you back from coming up with strong ideas. If you make up some lines that the character is THINKING as they are doing their performance, it can be a huge help in coming up with timing, facial expressions, gestures, etc.
Hope that helps someone! Thanks for swinging by the blog!