My birds never really bit me cause I was working with them since they were very young. The only trouble I had with Kili was biting other people or Truman which I spent a lot of time resolving. The only time either has bitten me was not realizing me, in a panic, or while looking at the other bird.
I didn't condition Truman to touch gradually. It was just like in this article. One session to teach and then a few to solidify.