Play C as the fundamental tone. C is open--no valves are pressed down.
Play the next pitch in the scale while pressing valves 1 and 3. This note is D.
Proceed to the third note of the scale (E), by pressing valves 1 and 2.
Play the fourth note of the scale (F) by pressing valve 1.
Play the fifth note of the scale as open--no valves down. This note is G.
Proceed to the sixth note of the scale, which is A, with valves 1 and 2 down. Note that these notes are getting higher and you need to tighten your embouchure.
Play B with the second valve depressed for the seventh note of the scale.
The final note of the scale returns you to open valves and the note C.
Play the scale backward so you end back on C, the same note with which you started.