This is easily the most common rhythm pattern in blues guitar. It's also very common in rock and pop music. Learn the keys of A and E first since they use open chords and are easiest to play. Afterwards, if you learn it in the key of G, you will then be able to play it in any other key just by moving your chord shapes along the fretboard. This can be played at any tempo, but I recommend starting with a slow blues feel . For a blues sound, use a bouncy shuffle feel. For more of a rock sound, use a straight eights feel.