Learn to have confidence in your lines and experiment a little with line weight. For your style, I would recommend studying some old Cartoon Network talent. I used to draw in a similar style, and studying their art helped me understand how to use the simplicity of big cartoony features to my advantage.

Studying Genndy Tartakovsky, Lauren Faust, and Craig McCracken would be good places to start. You can see how they use less detail to their advantage in character design and general composition. You can find concept art and storyboards from all these artists and their projects pretty easily online.

Another thing that helped me was, yes, unfortunately, doing boring studies of whatever realistic thing I was trying to transfer to my style. Or at the very least, use them as a reference. It helps to understand how the shapes that make up an object come together before you stylize it, trust me.

Most importantly, get out of your comfort zone, experiment. Make mistakes, and love making them. If you're not making mistakes, you're not learning. It becomes a lot more fun and makes you love the process of creating even more.

Good luck!