First off you have to know which scale to use,and thats depends on the key the song is in. (this is where music notation comes in handy. The number of sharps and flats in the key sig can tell you). But you can always listen to the song and figure out the key.
Then once you figure that out, go to the desired scale in that key. Avoid the notes or bending dertain notes in that scale that sound whacked out played with the chord progression. Study the scales up and down the gretboard , the domniant forms and non-dom.