There's even a book on the subject by long-time busker Johnnie Mac, covering all the basics from the choicest locations to where to put your tip cup. Mac spent almost 20 years as a street musician and says he was, "making a fortune... in fact, more than triple what I was making in the job I left behind."
And there's plenty of room for advancement. The Blue Man Group, Jimmy Buffet, Pierce Brosnan, George Burns, Bob Hope, Jewel, Jimmy Page, Penn and Teller, Rod Stewart, Simon and Garfunkel, Bob Dylan and Robin Williams all started their entertainment careers on the streets.
This is none of the people listed above but he's probably loaded.
Sure those people all had talent, but you can also make money miming, fortune telling and standing totally still while covered in silver paint (though we're guessing that last one involves lots of smart-ass kids walking by and punching you in the nuts).
Street performances are perfectly legal in most places as long as they don't interfere with traffic and business. But you do have to deal with the other buskers who are trying to horn in on your racket. After all, your sweet saxophone playing isn't going to get you any cash if there's a dude noisily plucking at his banjo five feet away, drowning you out. Luckily there's a sort of "Busker Code" that street entertainers follow which basically states, "I got to this corner first, and if you try and set up shop here, I'll stab you."