Watch the Keith Richards online guitar lesson by Jeff McErlain from Kings of Tone
Open G is the key! Keith refers to his guitar in this tuning as the "electric autoharp" because of its relative simplicity for chording. When I first learned that most of my favorite Stones tunes were in open G it was a revelation. I could finally decipher what the heck he was doing. Just watch some of the footage of him playing "Brown Sugar", if you were in standard tuning his fingering would make no sense, like they did for me for years! So open G truly is the key to some of the Stones coolest riffs.