Circus is a physical art-form that can engender a sense of control just as any type of athletics or dance training can. However, unlike most physical disciplines, circus has a place for almost any physical type. It’s one of the few places where I’ve seen short powerfully built women valued for their bodies. The circus is associated with the carnavelsque, so it’s a great way to have a party or to disrupt social patterns. And circus is also a lot of fun.
Circus is still mainly an oral tradition. Moreover, for certain of its disciplines it is confined to very particular places that can rig the necessary equipment and safety devices. It would be, for example, impossible and probably immoral to write a book describing how to learn the flying trapeze. There are plenty of books and resources for learning the object manipulation arts, eg. juggling, stick spinning, plate spinning, diabolo, etc. A good place to start with these would be Juggling Information Services. However, most serious folks quickly move back to oral traditions.
The best place to learn new juggling and assorted object manipulation is your local juggling club. The Internet Juggling Database lists juggling worldwide, by country.
For the more physical circus arts and clowning, most big cities have enterprises that offer classes. The San Francisco Circus Center and Chicago’s Circus Factory are one’s I have experience with but I know there is instruction available in Boulder, CO; New York, NY; Seattle, WA; Atlanta, GA; Asheville, NC.
I think the best value however, if you have the time, are youth circus programs. Many big cities have non-profit programs that teach circus to youth. Many of these programs will offer volunteers instruction in the circus arts. The American Youth Circus Organization has a directory of youth circus programs.
I personally have not been too interested in the professional schools. They are more like the graduate programs.
Of course, working for a circus is not a bad way to learn either, and the way that most people, historically, have learned the trade.