Watch the Chord / Scale Theory online guitar lesson by Brad Carlton from Guitar Lab: I7 to IV7 Vamps
Chart 1 is a master chart of the major scales and their modes. In the key of C. C is scale degree I and F is scale degree IV. In major scale theory the only place that a dominant seventh chord is build is on the fifth step the scale. This means that when you play C7 chord, the key of the moment would be F major. You will be playing the V chord in the key of F which would utilize mode V which would is C mixolydian. Chart number two shows the C mixolydian mode with the guide tones highlighted in red. This same theory that has just been presented would apply to the F7 in your progression. The F7 would be the V chord in the key of Bb major (see chart 1). So from a theoretical standpoint, when you change chords you change keys. To summarize this theory, the C7 is the V chord in the key of F and the F7 is the V chord in the key of Bb. Therefore your modes are C mixolydian and F mixolydian. Chart number two shows how the notes function in each of these modes. The C blues scale is also presented in terms of scale degrees. Chart number three is very important because it explains how each note that you play over the I7 chord will change meaning when played over the IV7 chord. Diagrams one through six display this information in the lower area of the fingerboard.