To lighten my hair I used 20vol creme developer mixed with powder bleach, to get it as light as I am now I had to do a few applications. I did it myself a few times spaced out over a couple of weeks, and then treated myself to some trips to the salon to get it done once it was getting really light (I don’t advise home bleaching though - if you don’t really know what to do it can end very badly, I’ve seen it happen to people many times!! :S)
Then, once it started getting reasonably light I started toning it to get rid of any yellow tones using Fudge purple shampoo (and I get a toner applied if I get my hair done at the salon).
To upkeep the white colour I just use the Fudge toning shampoo as needed to stop it going brassy, generally every second wash or so :)