Originally Posted by: radel.cookie... if the song is in the key of E, I will always play in the E pentatonic ? Or when someone hits a C for example, I need to change for the C position ??
If all the chords in the song are in one key, then you can play within that one key (or scale) throughout the chord progression. If the progression changes to a chord containing notes outside of the key, then you adjust the scale or change the notes to play over that chord when it happens.
I cover this in detail in these lessons on improvization:
http://www.guitartricks.com/tutorial.php?input=876
http://www.guitartricks.com/tutorial.php?input=483
http://www.guitartricks.com/tutorial.php?input=491
If the chord is far enough outside of the key, then you can or might have to use a different scale while that chord, or group of chords is happening. I cover that, more advanced idea, in these tutorials on jazz guitar.
http://www.guitartricks.com/tutorial.php?input=519
http://www.guitartricks.com/tutorial.php?input=1205
What all that in mind, I don't want to point you to lessons that you can't use. If that stuff is beyond your current knowledge & skill level, then you should probably work through the Guitar Fundamentals courses. They have more basic lessons on how scales & chords are related to each other.
http://www.guitartricks.com/course.php?input=1
http://www.guitartricks.com/course.php?input=2
Hope this helps! Ask more if necessary. Have fun. :)
Christopher Schlegel
Guitar Tricks Instructor
Christopher Schlegel Lesson Directory