This is a variation on a famous James Stamp exercise.
Use a metronome. Set it to MM=60.
1. Do this as a breath exercise. HOOO feeling.
2. Do it as a buzz exercise with glissando. Slide from note to note.
Take in air on count 4 (after breathmark) and close lip with "UP". Start the buzz with a POO attack. Do it very soft. Try to use the same feeling as when doing it as a breathing exercise (1).
3. Do it with legato and centered tones.
4. Do it with TOO attack and without legato.
Note: If you can't do the whole exercise at first,
work on it! The last bar is excellent for developing lower lip strength.