Watch the Triplet Rhythms online guitar lesson by Massimo Varini from Pop Guitar Survival Guide
Playing in triplets changes the pick direction every fourth beat. On the first beat we'll start with a downstroke, on the second beat we'll start with an upstroke. It's very important to pay attention to have the same weight on both directions: down and up. We can also play the triplets using what I call the circle of three: three strikes (DUD Down Up Down) as a pattern.