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I currently added life drawing to my daily drawing practice. I usually draw portraits and study anatomy. What else should I do? I want to be eventually good at cartooning.
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Try occasional sculpting, it can be an eyeopener to see what cartoonish figures look from all sides and how to construct them to look reasonable from all sides. It forces you to take something flat (like, a cartoon character), and make it work in 3D. Also you can use them as references.
Also anything you want and feel that you need. Look at good cartoon images and see what they have. Do they have good colours? Maybe you should consider practicing that too eventually. Good lineart? Practicing inking techniques won't hurt either and so on and so on. However you really should put time into learning the basics of constructing your characters from simple objects. Draw objects like balls, squares, triangles. Your characters and other objects will be created from the simple shapes.
If you want to do cartoons, then gestural drawings will help massively with expression. Do quick life drawings of anything, focus on capturing expression.
Study different comedians. Look at Chaplin and Keaton. Learn about joke structure. What is drawn in the cartoon matters only if it makes that joke work.
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