One good exercise is to start with simple stick figures to get the proportions right. Then, add more details like facial features and clothing.
Start by doing gesture drawings to understand the flow of the body. Another useful exercise is to draw a single person in multiple poses to improve your understanding of anatomy and perspective for cartooning people.
One useful exercise is to practice sketching simple shapes and figures repeatedly to improve your line control and proportions.
You could try contour drawing. Focus on the outline of an object without looking at your paper, it helps improve your observation skills. Also, practicing shading and adding texture to your drawings can enhance the overall look.
One simple exercise is to start with basic shapes like circles and squares and then combine them to form simple characters. Another is to copy simple comics to understand the flow and composition.
Stretching your hands and wrists is a good start. Also, doing some simple shape sketches like circles and squares can help loosen up.
One useful exercise could be to describe a character's day in detail based on a random prompt. This helps build descriptive skills.
One effective exercise is practicing character poses. You can look at reference photos or use a mirror to try different poses and then draw them. This builds your ability to create dynamic characters. Also, doing gesture drawings helps you capture the movement and energy quickly.
Simple yoga poses like the tree pose or the cat-cow stretch can be fun for kids as seen in some cartoons. These help with flexibility and balance.
For comic inking, practicing drawing smooth curves and straight lines repeatedly is essential. Another useful exercise is inking over existing sketches to focus on the line quality and consistency.
You could try writing a story based on a random prompt or word. It forces you to think creatively and come up with unique plots. Also, doing character sketches of fictional people you invent helps flesh out your characters and make them more believable.
One could be 'What if the main character had a completely different upbringing?' This can lead to new plot developments and character insights.