I'd like to play some eric johnson or joe bonamassa scales , how could I proceed to learn and with which methods and mediators

There are plenty of tab and lesson books of Eric and Joe's songs and style. Start there.

Eric Johnson:
http://www.google.com/products?hl=en&q= ... CB8QrQQwAg

Joe Bonamassa:
http://www.google.com/products?hl=en&q= ... CCcQrQQwAg

_________________
Obligatory gear list: Fender, Rickenbacker, Gibson, Gretsch, Vox, Martin, and more Fender.

Start by getting your major/minor pentatonic scales nailed in all 5 positions, then work out ways of linking them together. Work on 'cascading' the pentatonic notes in groups of 3,4,5 and 6 up and down.

For more exotic stuff, do some work on your modes of the major scale, and try moving some of the notes around within the pentatonics, e.g for a nice EJ sounding scale, play the minor pentatonic but raising the minor 3rd to a major 3rd. Sometimes called the hindu scale I think.

And both Bonamassa and EJ have Cream-era Clapton as a major influence, so you could do a lot worse than study that.

Indeed... as EJ says in one of his DVDs, "start simple, and start slow"

Excellent advice.

The fact is, if you can't play it slow you can't play it fast. And however fast Joe in particular plays, his passagework is exquisitely clean and accurate - no sloppiness in sight. That only comes from years of careful painstaking practice.

Let's get started...!

Cheers - C