Dressing up like Jimi Hendrix and wailing on a guitar doesn't quite cut it. Also remember that an instrument is not necessary. If you have a good voice, sing for people. Location is the key to every good business. Some bums have their territory at Store 24 where they will open the door for you when you leave or enter in hopes that you will give them your change.
Some bums wait in subway stations.
While others try college campuses. Choose wisely because a bad location will get you nothing. That makes me want to pop you in the mouth. No matter what gimmick or combination of gimmicks you use, make sure to make it as original as possible. The best example and most famous example in Boston is Kenmore's own Mixed Nuts.