Watch the Both D7 Positions online guitar lesson by David Hamburger from Fingerstyle Blues Factory
In more rustic environs, chord voicings are sometimes known as “grips.” It’s a great image, and actually speaks to a real truth about learning your way around the neck: you’ll know you’ve got a new chord voicing under your fingers for good when you can just reach for it and find all your fingers falling into place at once - just like gripping a coffee mug or a ballpoint pen (or, I suppose, a smartphone - but that would mean letting one out of your hand in the first place. Most unlikely.) While I like to think this lick stands on its bluesy merits alone, it also serves as a great exercise in getting these two voicings to be second nature. In addition to working your way through the lick, you might also try just shifting from one voicing to the other, back and forth - from grip to grip, until your fretting hand knows them as well as a C or a G chord.