Watch the Sixteenth Note online guitar lesson by Brad Carlton from Guitar Lab: Shuffle Secrets
This lesson deals with 16th note triplets which are twice as fast as eighth note triplets. A good way to count them is to change how you label each eighth note triplet. Instead of counting: one trip let, you can count: one two three. Then to subdivide each eighth note of the eighth note triplet into a 16th note you simply count: 1+2+3+. 16th note triplets can also be thought of as sextuplets, which means you are playing six notes in each beat. Therefore you could count them: 123456. Just remember that the one will correspond to the quarter note (the tempo).
You will receive a drum groove track which will establish this rhythmic concept. Spend time counting and playing along with the track so you are rock solid in your understanding of this rhythm.