Watch the G7 Blues online guitar lesson by Rob Garland from Melodic Soloing: Blues Chord Tones
Look at the movement of the 3rd of G7 here, the note B. I played just the 3rd and moved it to the b7th of C7, Bb. Then, I moved it up to the note C (the b7th of D7 chord). Look at where these notes are in the chord voicings. Be sure to play along with the jam track and hear the notes move.
Then, listen to the movement of the note F (b7th of G7 chord) to E (3rd of C7 chord). Then up to the note F# (3rd of D7 chord). And once again look at the chord voicings.