Watch the Outlining I-IV-IV Without Jam Track online guitar lesson by Rob Garland from Melodic Soloing: Blues Chord Tones
So what did I play? I aimed for the major 3rd of the C7 chord with a major pentatonic style lick that included the 5th, root and major 3rd. For the quick IV chord, F7 I played the Eb note, the b7th then back to E for the C7. Sometimes one note is enough to outline a chord change! Then, I went back to the original theme on C7 and targeted the 5th of the F7 chord with a bend.
For the V chord, I played a doublestop (2 notes) taken directly from the G7 chord voicing grabbing the 3rd and root and walked that down to the 3rd and root of the IV chord. I attempted to copy my opening idea in a lower register on the C7 chord and then just landed on the B note for the G7 turnaround, the 3rd of the chord.
This was just one improvised 12 bar. Make sure you experiment with playing in different areas of the neck and different keys, trying to outline chord changes without a jam track. Once you've done this go back to using the jam track and you'll be surprised how much more melodic your solos sound!