A variation of the R.J. Lockwood groove.

Wrap your hand around the neck and use your thumb to play the tonic.
Beat 1 incorporates a feature that is used a lot in blues.
You play the minor third of the chord first and then immediately hammer on the major third with your middle finger.

That minor third creates a bluesy sound, because it is a part of the blues scale.
The chord is a major chord. The best of both worlds.

In this groove you’re actually playing two chords where you’d normally play only the tonic.
In fact you’re alternating continuously between the I chord and the IV chord.

Keep your hand wrapped around the neck and play this IV chord with your ring finger.

Move this grip 5 and 7 frets up to get the IV and the V chord.

You can also use inner logic to remain in position (chorus 2).