Established cartoon material has been moderately successful. "The Simpsons" and other Simpsons- related comic books have done okay, but they fail to capture the kinetic manicness of the TV show. Similarly, "Ren & Stimpy", "Beavis & Butthead" and "Aladdin" were all moderate hits, but failed to capture the necessary qualities of the characters' voices. All of these examples are from the 90's, but a look at any of the cartoon based comic books of the past reveals a more important factor. The intrinsic problem is that when people lose interest in the cartoon, cancellation of the comic is sure to follow. Only such stalwarts as "Mickey Mouse", "Donald Duck" and "Archie" can lay claim to lengthy runs.
Fantasty comics based on previously established material have maintained a mediocre presence in the market. Marvel's "Conan the Barbarian" lasted for 23 years. But the various Conan spin-offs of the 1980's were pretty dismal. All of the TSR property Dungeons and Dragons comics were short-lived.
Conversely, fantasy comics based on original material have done quite well, particularly by independent companies. Dave Sim's Cerebus (Aardvark-Vanaheim) is over two-thirds of the way through its projected 25 year run. Wendy and Richard Pini's Elfquest (WaRP Graphics) has been chugging along for twenty years now. Most recently, Jeff Smith's Bone (Cartoon Books, 1991- present) has made its mark in comic shops. I would posit that original fantasy comics have garnered more success as the authors actively promote their materials and are more responsive to their fans.
How to Cartoon

The following resources, both online and print, are helpful for the cartoonist who wants to learn how to improve his art or his chance of making a living from it.

Your Career In The Comics by Lee Nordling. Anyone seriously interested in being a cartoonist MUST buy the book Your Career in the Comics by Lee Nordling. It's about $8, and contains wealth of information about the business issues cartoonists face when playing the syndicating game. You can get it at some bookstores, or from Amazon.com through the above link.
Duane Barnhart's Cartooning Basics : Creating the Characters by Duane Barnhart and Angie Barnhart.

This useful guide with over 500 illustrations is an entertaining and humorous book filled with easy to follow suggestions that assure that even beginners - young and old - can produce successful cartoons. Duane is a professional cartoonist who has been published in "the Saturday Evening Post", his own syndicated comic strip, and many childrens' books. This book is based on Duane's teaching cartooning in schools and art centers as an artist in residence. Charles M.Schulz, Creator of Peanuts, wrote the foreword, and initial response indicates the book will become a standard reference in cartooning and teaching.