Water's down pat. Actually animating anything more complicated than a single rigid body is still strange though. Waving hands? Wavy fish? Kind of complicated for now. At any rate, rigid bodies still are a little complicated, so I delved into how Blender's physics system worked to help me create piles of stuff for scenes and animations.
The fun thing about Blender (and I suspect all 3D programs do this in some way) is that you can start off a scene with a big floating pile of stuff, run some physics to have it all become a messy pile on the ground, and then freeze it there to help make natural looking background elements (piles of glass bottles in a potion shop, for example).
As for making more compelling foreground objects, I looked a bit into rigging. This is definitely a rough first-pass, since I'm planning on making a fully-fledged rig one day, but I learned enough to make some template sketches, turning them into rigs with simple skeletons that allow for more complex motion.
This last piece was inspired by a very good 2D drawing done by @TwiIi_Princess on twitter. Getting to make it means I've reached a pretty good point in learning Blender, since it was one of the first things I really wanted to model out and animate.