Some insight into the way I work with animation sheets.
Iterating with an artist over a sprite sheet can be really hard if you don't have a proper methodology in place. At first I used to incorporate the new animations myself because I haven't proposed any structure to the game sheets.
Bear in mind that the order of each animation is important because that is translated into a JSON file and then fed to the game's logic. If you switch or misplace by 1 pixel something then it will look wierd on the canvas.
The key take-away here is to setup and agree a workflow that is easy for you and the artist(s) to iterate. If could:
provide a template with placeholders (eg. Idle animations 6 frames of 64x64)
provide guidelines about maximum width and height a sprite can be
specify if the shadow of the character needs to be separately (or on a separate layer)
leave the artist free to self-organize, don't micromanage as the changes can prove to be costly (time, money, effort)
Here is the full game dev video log: