Man, what's all this key stuff and scales in rock. The key is either E, A, or F# and then just lay down its respective minor scale ontop of all the chord changes. If it's major (haha right) take the root note and go down 3 frets from it and play that minor scale, it'll work.

If you don't know what key a tune is in, play the first chord in the chorus. That's the key. Then pound that chords minor scale over top of everything. boom.