An essential rhythm playing technique every guitarist should learn is what I call eighth-note “pendulum” strumming. It involves keeping your pick hand constantly moving down and up across the strings in a steady, unbroken eighth-note rhythm – “1 and, 2 and, 3 and, 4 and” – with downstrokes on the downbeats and upstrokes on the upbeats (the “and” counts).
The movement is comparable to that of a pendulum on a grandfather clock that swings back and forth, the only difference being the horizontal orientation of your arm, as opposed to the vertical hang of a pendulum.