Originally Posted by: SvanholmLets say that me friend plays a 12 bar blues in the key of E and I improvise a solo on the E blues scale.
When he change to A-chord or B-chord, shall I change to the A or B scale or does the E scale works the 12 bar?

You can do either.

In general, most blues just stays within one scale as the chords change.

Slightly more complex blues players will target chord tones. This means you mostly just use one scale, but use the notes of that scale to emphasize the notes of each chord as they happen.

Still more blues players approach it more like a jazz player, they totally follow the chord changes & alter the scale as necessary.

These tutorials are on the basics of improve & following the changes within a scale.

www.guitartricks.com/tutorial.php?input=876
www.guitartricks.com/tutorial.php?input=483
www.guitartricks.com/tutorial.php?input=491

These tutorials show you how to do it within the context of blues.

www.guitartricks.com/tutorial.php?input=217
www.guitartricks.com/tutorial.php?input=826
www.guitartricks.com/tutorial.php?input=232
www.guitartricks.com/tutorial.php?input=244

Hope this helps!