To tongue well, it is very important to maintain your tone while moving your tongue. A good way to practice tonguing is to say it out loud using Tah, Too, or Toh (whichever you prefer).
When you say it out loud, you will notice that you keep the sound going continuously as you tongue. You don't stop the sound for each note, but instead keep the sound going while you tongue through the sound. This is the concept you want to copy with your tone when you play.
Now try it on your horn. Play a whole note for 4 full counts, stopping on beat 1 of the next measure. Next, play 4 quarter notes and tongue them as if you were slicing the whole note into 4 parts. You want to tongue through the whole note tone for your 4 quarter notes. It will sound choppy if you stop your air for each quarter note as an individual note.
As you learn to tongue faster, make sure you keep a good vowel sound (Tah, Too, or Toh) to maintain your tone. If you have trouble tonguing faster, say it out loud and listen for a Tuh sound instead of a Tah, Too, or Toh. Tuh is a bad vowel sound. The more you hear Tuh, the more you are closing your throat and losing your tone. This also shuts your tongue down so it won't move quickly. You must replace Tuh with Tah, Too, or Toh. Learn to say Tah, Too, or Toh out loud faster with no Tuhs at all. You must turn any Tuh into Tah, Too, or Toh to tongue fast and keep it sounding clean and clear.
You now need to learn to say Tah, Too, or Toh as fast as you want to tongue. It is much like a tongue twister such as "rubber baby buggy bumpers". You must practice saying it out loud until you can say it as fast as you want to go while keeping it in rhythm and clear sounding. Do the same with Tah, Too, or Toh until you can say it fast without any Tuhs at all.
Your tongue will feel firmer when you say a good vowel sound like Tah, Too, or Toh because your throat is open as it should be for a full tone. Your tongue is easier to move when it stays firm. It is not tense, but it does feel firm. You can't have a firm tongue without an open throat or vice versa.
Maintaining your tone keeps your tonguing clear and clean, no matter how fast or slow the speed.
Copyright Norlan Bewley 1999