Once you are comfortable soloing using the chord tones, you can begin to fill in the space between them with notes from the scales. In this song, the three scales needed are C mixolydian, F mixolydian, and G mixolydian.
What is mixolydian? There are two ways to think about it:
The first way is probably easier to remember. To find C mixolydian, just play C major and lower the 7th note B to a B flat. Voila – C mixolydian. This is all demonstrated in the video below.