First of all, the Episode Guide even talks about this issue:
This is a tutorial on making your scene more smooth and making a character start an animation while another character speaks.
After a character finishes talking, they will be in the end of the pose (also, let’s say if you use talk_gesture with character A, if you click the screen too fast they will still be doing talk_gesture as character B talks). You may notice character A is still doing the end of the animation of talk_gesture as character B speaks. It will look extremely awkward as character A’s arms are outstretched towards character B who is, let’s say, giving a speech. What if character B calls them an idiotic monkey and character A is still just smiling there, still in the end of the animation talk_gesture since you, the writer didn’t make them start another animation? Why is character A smiling and has his hands out while being insulted?! Fix this, by making character A do a bunch of different animations while character B speaks. This will bring your animated story more to life because readers will be bored of seeing their facial expression not change after many lines of dialogue. Sometimes the animation they were last in even looks awkward. You do not want them frozen in one animation for so long. Go for awesome, not awkward. Dazzling, not demonic. Excellent, not eye shattering 
- Make the character do a different animation after they say a line of dialogue and before the other character speaks.
HOW TO: Have a character do an animation while another one speaks:
Example:
&CHARACTER B is listen
CHARACTER A (talk_angry)
You are an idiotic monkey.
OR
@CHARACTER B starts listen
B
CHARACTER A (talk_angry)
You are an idiotic monkey.
&CHARACTER B is listen = @CHARACTER B starts listen
When it comes to animations, using & or starts means they (in this case CHARACTER B) will do the animation at the same time CHARACTER A is talking.
1.
Example of a Bad Script And Why
BAD script:
JERK (talk_exclaim_yes)
Then that’s what I’ll have.
JEM (talk_explain_neutral)
A cheesecake with strawberry cream it is.
JEM (talk_exhausted)
That’s what you’ll have for your grand birthday.
WHY it’s bad: It’s extremely awkward as the character is stuck in the talk_exclaim_yes_happy animation. The girl in the first panel’s pose is also off. It looks very strange.
Fixing the Bad Script
JERK (talk_exclaim_yes)
Then that’s what I’ll have.
#make JERK start a non-talking animation. Use & or starts
JEM (talk_explain_neutral)
A cheesecake with strawberry cream it is.
#make JERK do another animation to make your story more animated.
JEM (talk_exhausted)
That’s what you’ll have for your grand birthday.
2.
GOOD script + why
GOOD script:
&MOM is idle_shiftweight_neutral_loop
HOPE (talk_exclaim_yes_happy)
Yes!
&MOM is idle_awkward_scratch_loop
HOPE (talk_primp_neutral)
Finally freedom.
&HOPE is react_shocked_gasp
MOM (talk_handsonhips_neutral)
I’m sending Robert with you.
*remember to adjust zooms and speechbubbles accordingly. Also you can put the character who’s speaking at a higher layer, and then when they’re not speaking, at a lower layer.
WHY it’s good: After a new line of dialogue, the mother does a different expression in response to what her daughter says. The girl also does a new animation instead of staying stuck in the previous animation.
3.
Looping Animations + Extra Stuff
By the way you want to avoid this in your script as well (picture from the Episode Guides):
So aim for a nice flow, not an awkward one.
Helpful Resources to check out
Appreciation Thread For Jem! ❤ - #25 by JemU776
https://www.dara-amarie.com/guides
You can also find a bunch of tutorials on epyxmagic 
Hope this tip helps! Have a great day 
