If you want to get better at drawing: be it cartooning, comic books, or even painting realistic seascapes, the best way to learn is by copying those works by artists better than you.
Who is better than you? The same guys who are better than me, but a good starting point is any artist whose work you personally feel speaks to you. For me, that's fine artists like Toulouse-Lautrec, Sheile, and Klimt. I also llike the works of illustrators and cartoonists like Tex Avery, Chuck Jones, Rod Scribner, Disney, Vernon Grant, Frank Frazetta, and Robert McGinnis. But what I like isn't necessarily what you will like.
And that's okay. Pick the artists you like.
But the trick isn't in who you copy but in how you copy. A method for taking apart and putting together those works of art is what will help you analyze and understand what that artist is doing and how he or she is doing it.
For that, I recommend two books. 1) Cartooning by Preston Blair, and 2) How to Draw the Marvel Way by John Buscema and Stan Lee.
If I had to add a third to the list, it would be this little known treasure: An Approach to Figure Painting for the Beginner by Howard K. Frosberg.
When copying, it is essential you don't just go through the motions and processes outlined in those books. It is imperative you do your best to copy exactly. After you finish, compare your final to the original. Make an effort to write down what is different between the two. It helps if you hold your drawing up in the mirror. After you notice your mistakes, fix them!
Everyone makes mistakes. Even the best. What separates the great from the good and bad is the great don't settle. They work hard. And that means fixing what is not right.
The Mickey Mouse drawing is thanks to a model sheet I found on this amazing website.
The first (and best edition) of Cartooning by Preston Blair can be downloaded for free from here: pt 1, pt 2.
UPDATED LINK TO PRESTON BLAIR BOOK - http://www.animationarchive.org/?p=2091