There are four different ways you can play this song.
1. Play the melody (Audio 1)
This is quite obvious of course. You can play either the top line or the bottom line, as I also play the melody on the Play-a-Long track.
2. Invent a 3rd line harmony (Audio 3)
Experiment with a third harmony line, either below or above the two written parts on the score. (The track plays C7, F7 and G7 chords,use scale-tones from their respective Mixolydian modes.)
3. Fills on the long notes (Audio 4)
Play little counter melody segments over the long notes, especially at the end of each phrase. But keep it simple and be careful not to overdo it.
4. Full out improvised solo (Audio 5)
The melody also functions as a perfect backing riff. You can solo freely over it and try to react to the riff.
The Play-a-Long alternates choruses with and without the riff in the background.
(Down - Up - Top - Links)
BS 4. Scales for Improvisation