Honestly, I learned how to draw hands (and the body in general) by studying how other artists applied fluidity.
I'm talking curves, circles, bending, flexible shapes. Even though we can have square and rectangle shapes in our bodies, humans are basically soft, squishy beings that bend and twist and just...look soft. It's a mixture of taut and loose that helps the most.
And I found that my best hand motions and body gestures were the ones that embraced both. I look at paintings done by Jean Auguste Dominique Ingres and William-Adolphe Bouguereau, but I also looked at creators like Danny Antonucci (Ed, Edd, n Eddy), Emily Carroll, and Naoko Takeuchi (Sailor Moon).
Instead of breaking up the body into squares, I'd suggest breaking it up into lines. This first sample below kinda does just that -- showing the gestures in motion with sort of a silhouette look. I do a mixture of sharp and curved lines to show what parts of the body bends and what parts are taut with tension:
Then I do the same with the other two examples, though now, they're more detailed. Another suggestion here is to do looser drawings. Let you pen do one quick stroke, even if the poses aren't always anatomically correct:
The same can be applied to hands. I do a combination of taut and curved gestures, even a little bit of uncanniness. I might use my own hands for references and just exaggerate as I go along: