Level 1 Exercises
(Do not discount their simplicity! Here you have the principals of animation, which all other animation is built on. They are worth your time and effort.)

Ball Bouncing in place, no decay (loop)
Ball Bouncing across the screen
Brick falling from a shelf onto the ground
Simple character head turn
Character head turn with anticipation
Character blinking
Character thinking [tougher than it sounds!]
Flour Sack waving (loop)
Flour Sack jumping
Flour Sack falling (loop or hitting the ground)
Flour Sack kicking a ball

Level 2 Exercises
Change in Character emotion (happy to sad, sad to angry, etc.)
Character jumping over a gap
Standing up (from a chair)
Walk Cycle [oldie but goodie!]
Character on a pogo stick (loop)
Laughing
Sneezing
Reaching for an object on a shelf overhead
Quick motion smear/blur
Taking a deep breath [also tougher than it sounds!]
A tree falling
Character being hit by something simple (ball, brick, book)
Run Cycle

Level 3 Exercises
Close up of open hand closing into fist
Close up of hand picking up a small object
Character lifting a heavy object (with purpose!)
Overlapping action (puffy hair, floppy ears, tail)
Character painting
Hammering a nail
Stirring a soup pot and tasting from a spoon
Character blowing up a balloon
Character juggling (loop)
Scared character peering around a corner
Starting to say something but unsure of how

Zipping up a jacket
Licking and sealing an envelope
Standing up (from the ground)
Pressing an elevator button and waiting for it

Level 4 Exercises
Character eating a cupcake
Object falling into a body of water
Two characters playing tug-of-war
Character dealing a deck of cards out
The full process of brushing one’s teeth
A single piece of paper dropping through the air
Run across screen with change in direction
Sleeping character startled by alarm then returning to sleepy state
Opening a cupboard and removing something inside
Putting on a pair of pants
Opening the “world’s best gift” and reacting

Any of the above exercises using a very heavy character/object next to a very light character/object. Enhance the differences the weight change makes!
Things to keep in mind:
Reading these exercises will do as much for you as reading about push-ups would do for your physical muscles: NOTHING. If you want the benefit, you must animate them. Take a deep breath and just do it.
Do not forget the famous words of Ollie Johnston: “You’re not supposed to animate drawings [3D models]. You’re supposed to animate feelings.” If a character isn’t thinking, they aren’t alive, and the animation has failed.
Keep it simple! There is no reason to over complicate any of these exercises. Going back to push-ups, would push-ups be harder if while doing them you also recited the Gettysburg Address? Yes. Would they be any more beneficial? No. Keep things nice and simple and clear.
Do your best. There is no reason to do these exercises poorly. Give it your all. You don’t have to show anyone, these are for you. You owe it to yourself to try your very best. Something not quite right? Take the time to fix it.
As always, have fun. Push ups are not fun. Animation is supposed to be. Be joyful in your work!