Watch the Highway Key online guitar lesson by Jeff McErlain from Essentials: Chord Tone Soloing
The parent scale on this tune is the A minor blues scale, so as usual, mess around with that and get comfortable with it on this chord progression. I'm assuming that won't take much effort on your part, but it's essential. In the solo, I've prepared for you I take a classic approach and pay careful attention to how I outline the three chords in one position around the 10th fret. This position is really magical on the blues, especially when outlining the changes and looking for chord tones. They sit very well on top of each other here and it's also where many classic solos are performed in the key of A. Obviously, this is instantly transposable to any other key and I highly suggest you do that.
To start, after messing around with the A minor pentatonic scale, try using a major pentatonic scale on the A chord, and when switching to the E7 chord, keep on the major pentatonic scale. When you get to the D7 chord, try hitting either the F sharp note or the C natural, which is not in the A major pentatonic scale, but is in the D7 chord. That's a particularly strong note between these two and if you get that one, you're well on your way. Make that the goal of your practice session at first, just getting that one note that's different that outlines the changes. If you take these baby steps, I can guarantee you the results will be much better than trying to do it all at once.