Recently I updated the articulation packet on my website. Preference is given to working on articulation within music, but there are times when isolating the act of tonguing is helpful.
Assuming one’s air is supported properly, the embouchure is stable, and the player does not lack in endurance, the biggest issue is not tonguing speed. Rather, it is the learning a myriad of releases and lengths appropriate to any given musical style. Too many players, in their pursuit of higher/louder/faster, believe tonguing to be solely about speed. Yes, a quick tongue is necessary. But truly, articulation is a musical device. We must incorporate into our tonguing arsenal a wide variety of articulation styles—from uber-legato to semi-detached to marcatissimo—and everything in-between.
Finally, note that directions for these exercises are given in lessons, but do not appear in this packet.