Watch the Hot For Shuffles online guitar lesson by Angus Clark from Hard Rock Survival Guide: Rhythm
The most important part of this exercise is the muted shuffle picking on the A string. If you can get that feel happening then you've got the better part of the lesson. There are a few chord voicings of note. One of my faces is the A7#9 voicing you get in the 2nd bar. You use a voicing across the top four strings at the sixth position against the open A string. Very economical and effective. I'm doing a lot of chording just using 4ths on the third and fourth strings against the open A as well. During these sections I think of the chord stabs as similar to horn hits. You want them to pop. When we finally get to the IV chord in the blues form I'm using my stock Dom7/9 chord voicings with the root on the fifth string. Everyone should know these, so take a minute to get them under your fingers. You'll find a ton of uses for them, even if they are jazzy. There's a little figure just after the D chord that is signature to this rhythm part. I uses a broken A chord and a little riff on the A string where we hammer from the C to the C#. This motion from the b3 to the 3 of the chord is called an approach note, and it gives us a really bluesy quality in the rhythm part. The figure closes with a little move from the A chord on the 2nd fret to the open G chord and back again. Again I'm thinking like it's a horn part, so it's punchy and the mix of staccato chords vs. held chords is really important. The key to this Van Halen style, which is similar to the Pat Travers and Ronnie Montrose thing, is the silence between the chords. Pete Townshend is a great proponent of this concept, although the application is very different. You create the sense of tightness with the band by embracing the fact that how you come off the chord is just as important as how you attack it.