I break my practice routine down into 4 distinct parts: 1. Tone 2. Technique 3. Improvising 4. Composition. Today, I'll give you an effective exercise to improve your sound and control and yes, it involves long tones.
First, set up your metronome and tuner on your music stand and have them both on :) Set the metronome to 80bpm. Pick a major scale - it doesn't matter which one - and start in the middle of the horn. For the sake of clarity, I'll pick C major and start on C without the octave key. Take a big breath - really fill your lungs with air - and play the middle C as softly as you can. Play the note for 16 beats, with a gradual crescendo to as loud as you can play (with a nice sound) by the 8th beat. Gradually decrescendo to as softly as you can play with a nice sound over the next 8 beats. This should all be done with one breath while you are looking at the tuner to make sure you keep the pitch centered during the entire exercise. Do not move on to the next note in the scale until you have played this one perfectly. Repeat this for every note in the scale up to the very top of the horn (high F) and back down to the bottom of the horn (low B) and back to middle C.
Not so easy, is it? Here's the deal: if you practice this exercise daily, and really make sure that you are controlling the sound, playing the dynamics, and staying in tune, this one exercise will dramatically improve your sound, your intonation and your control. Not many people have the discipline to do this but if you stick with it, it will pay dividends!