YouTube is like the new music business: it's very hard to breakthrough, and I'm not sure if there's a formula for it. There's definitely a bit of luck involved.
John Densmore (drummer for the Doors, whose last hit was in 1971) once described what it takes to make it in the music business then and now:
1) Pounding the pavement to make yourself known. You have to hustle so people know who you are.
2) Luck. The Doors happened to be in the right place at the right time.
3) Talent. Just like the other bands that broke out at the same time as The Doors, Love, (led by the songwriting of Arthur Lee) Jefferson Airplane (songwriters and stage presence of Grace Slick, Marty Balin, and Paul Kantner, plus the instrumental powerhouse of Jorma Kaukonen, Jack Cassidy, and Spencer Dryden), and Buffalo Springfield (Steven Stills, Neil Young, and future Poco founder Richie Furay), these bands had talent to burn, but still needed to hustle to break out of San Francisco or L.A.