Using the method on this site.
Seriously- I had despaired of ever teaching her how. She could fall with training wheels!
A few weeks ago we tried without training wheels and she was so wobbly that I had to literally hold her up.
Three times of trying it this way and she's riding!
I am SO PROUD!
Also, I think it's kind of a classical approach.
Work on skills in isolation, then combine and reap the rewards.
I'm so proud. :)