ahh omg!! thank you!! i struggle with that a lot actually!!
loosening up is hard, but here are some tips!!
1. do some figure sketches with charcoal, or if youre using a pencil, a great way to loosen up is to hold the pencil further back from the tip, and use grander gestures, drawing with your whole arm, rather than your wrist.
2. draw the line of action in your figures first! make your figures really exaggerated in their body movement! focus on the silhouette, make sure there is good negative space in their pose, that you would be able to tell what the pose was if the whole figure was colored in black!!
3. try doing a drawing where you only use curved lines, no straight lines!
4. draw dancers! drawing ballerinas, and really actually trying to draw them in all their fluid glory really helps! the best thing i’ve ever done is study and then animate a ballerina jumping, theyre just so fluid and graceful, it imitates in your art.
5. this kind of goes with exaggeration, but try caricaturizing your people or animals or whatever you’re drawing
6. study real life and other artists that you find fluidity in!!
these are just things that work for me, if anyone else has any tips, chip in!!!
it all takes practice, but finding fluidity in your work is fun and youre gonna be great at it!!!